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AUDIO-VISUAL CONSERVATION at The LIBRARY .>f CONGRLSS
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for Audio Visual Conservation
www.loc.gov/avconservation
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JANUARY 1938
VOLUME 13 • NUMBER 1
25c A COPY • $2 A YEAR
A Message to Projectionists
We appreciate the confidence you have shown, over the last ten years, in the ability and integrity of our engineers. We believe that, over those years, we have learned thoroughly to understand your daily and emergency problems, and under the name Altec we will extend our cooperation in meeting those problems shoulder to shoulder.
We intend to do this without restriction as to contract or type of equipment. Our friendly relations of the past ten years continue with an even closer bond. You may call upon the Altec engineer as a friend— and that goes for all of us in Altec.
L.W. Conrow
PRESIDENT
THAT YOUR THEATRE MAY NEVER BE DARK
T«EB£ IS A NEW MME THAT MEANS BOX OFFICE INSURANCE TO EVERY EXHIRITOR
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Dan Bennett and Warner Baxter in Walter Wanger's Vogues of 7938"
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Write for interesting catalog and name of four nearest Independent Theatre Equipment dealer. He will, without obligation, arrange to Jemonstrate the Strong lamp in your theatre.
7L STRONG ELECTRIC Coty.
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EXPORT OFFICE: IOOM 2002, 220 W. 42nd ST., NEW YORK, N.Y.
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PROJECTION
provides the white light essential to satisfactory projection of the new color pictures which are being shot under lights having the same characteristics.
The Strong Mogul Lamp de- livers this flawless, steady, bril- liant light most economically.
January 1938
INTERNATIONAL PROJECTIONIST
A SUCCESS STORY
...THE STORY OF BETTER PICTURES
G-E Copper Oxides solved projection prob- lems for Mr. T. B. Noble, Jr., owner of the State Theatre, Inc., Oklahoma City, Oklahoma.
You, also, can end projection worries with G-E Copper Oxide Rectifiers. Theatre owners everywhere are patting themselves on the back for buying this superior equipment. They learn by experience that these Recti- fiers are synonomous with quality. Low operation costs and dependability insure satisfaction in G-E Copper Oxide Rectifiers for Projection Service.
To make your theatre 1 00 per cent modern, install G-E Copper Oxides. They will improve your pictures and increase your savings. Give your pictures that added clarity and bril- liance. You will boost your patronage.
Send this coupon now, and let us help YOU with YOUR projection problems. Mail coupon now for complete information
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INTERNATIONAL PROJECTIONIST
January 1938
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Todays critical audiences' demand for quality projection can best be met with Peerless Magnarc High Intensity Lamps.
In no other lamp is it possible to obtain so much value for first cost expenditure and such a great degree of purchase satisfac- tion after installation. The proof of this lies in the fact that Peerless Magnarc outsell all others two to one. High intensity projection has been found an absolute necessity by one-third of all theatres in the United States — and these theatres have 75 per cent of the total seating capacity of the country.
This modernizing of projection has been brought about mainly by Peerless Magnarc's ability to produce 200 to 300 per cent more light on the screen for the same current cost of low in- tensity lamps. Think what this means in better picture quality, audience satis- faction, competitive advantage. Then write for the new folder, "Get A Seat On The Bandwagon."
MANUFACTURED BY
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January 1938
INTERNATIONAL PROJECTIONIST
ROJECTIGNISI
With Which is Combined PROJECTION ENGINEERING Edited by James J. Finn
Volume 13
/
JANUARY 1938T
Number 1
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Film Aperture Decision Rests 111 |
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Outline of the Requisites for a Competent Projectionist .... A. C. SCHROEDER |
9 |
Some Television Problems — A Description for Laymen, II. . Arthur Van Dyck |
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S.M.P.E. Discussion of Stereo- |
13 |
Projecting Hi- and Low-Range Prints; Standard Fader Set- |
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14 |
24 |
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Analyses of Modern Theatre Sound Reproducing Units, II. |
academy of m. p. arts & Sciences |
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Aaron Nadell |
News Notes |
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Boston L. U. 182 Model Admit- tance Procedure is Thorough |
Technical Hints |
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19 |
Miscellaneous Items |
Published Monthly by
JAMES J. FINN PUBLISHING CORPORATION
580 FIFTH AVENUE, NEW YORK, N. Y. Circulation Manager, Ruth Entracht
Subscription Representatives
Australia: McGills, 183 Elizabeth St., Melbourne New Zealand: Te Aro Book Depot, Ltd., 64 Courtenay Place Wellington England and Dominions: Wm. Dawson & Sons, Ltd., Pilgrim St., London, E. C.4.
Yearly Subscription: United States and possessions, $2 (two years, $3) ; Canada and foreign countries, $2.50. Single copies, 25 cents. Changes of address should be submitted two weeks in advance of publication date to insure receipt of current issue. Entered as second-class matter
February 8, 1932, at the Post Office at New York, N. Y. under the act of March 3, 1879. / Contents copyrighted 1938 by James J. Finn Publishing Corp. International Projectionist is not responsible for personal opinions appearing in signed articles in its columns.
MONTHLY CHAT
FOR years we have been half-sold on the idea that we were directing our fact and fancy in the form of words, illustrations, ink and paper to one of the most unresponsive audiences ex- tant. Only when an occasional error crept into print, and we heard from the folks back home, did we waver in the aforementioned belief. But we've been forced to revise our opinion on this topic, because there is evolving out of our current Prize Contest a type of con- stituent heretofore unknown to this corner.
More than 200 projectionists (at this writing) bothered to write two- and three-page answers to the Contest ques- tions, including not a few drawings. And good stuff, too. To top it off, a manufacturer recently told us that his I. P. advertising netted him six times as many replies as any other medium. Really, we're beginning not to recognize our own people. Of interest is the fact that Contest replies from small towns outnumber by three to one those from alleged big towns. City fellers evidently are either too smart or too complacent or too near service facilities. The little- town fellow is pretty much on his own.
All of which compels a drastic revision in previous conceptions of the respon- sitivity of the projectionist craft.
REPORTS that a 9 mm. Suprex car- bon has been available for quite some time now are hereby declared to be erroneous. The new Suprex size probably will be larger, about 10 mm.
YOUSE guys what don't like the new I. P. cover shown publicly for the first time with this issue will oblige by stating why. We intended to revamp the inside too, but we're still quarreling with the printer about the purchase of new type fonts.
A TOP-FLIGHT Mass. official likes to view motion pictures from the cen- ter balcony — but must sit on the main floor because of projection room noise (mostly projectionist jabbering). How many such dissatisfied customers are there?
THE projectionist at a theatre in an isolated Canadian town runs a radio store as a sideline, on the letterhead of which appears this statement. "A good radio will keep husbands home at night."
PRODUCTION notes: West Coast technicians are trying to revive the wide film idea. At least one major com- pany laboratory is edge-waxing all prints, which practice has been repeated- Iv demonstrated to be harmful rather than helpful to the proiection process. Improving the Standard Release Print is great stuff — if the original specifications, particularly with respect to change-over dots, were faithfully adhered to.
INTERNATIONAL PROJECTIONIST
January 1938
QUALITY PROJECTION
AND THE
FACTORS OF VALUE
High quality projection means a good show — the kind of show the public wants — the kind of show that fills the seats.
Simplified High-Intensity, powerful white screen illumination, brings you this modern theatre essential.
BRENKERT
EN ARC *&££&
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gives you Simplified High-Intensity projection, plus these six funda- mentals of projection lamp value:
I • Economy in operation
2* Correct engineering in every detail
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4* Complete parts catalog service
5« Prompt, efficient factory service
O. Universal, dependable dealer service
Brenkert operates the largest plant in the industry devoted to Arc Lamp manufacture for mo- tion picture theatres — the only manufacturer producing all types of projection lamps for every theatre requirement and for cor- rect operation with all standard makes of projectors.
These are the factors that mean unparalleled performance and satisfaction — the better show. For these reasons, theatres of all sizes endorse and use Brenkert Projection Lamps — and Brenkert installations are increasing faster than those of any other make of lamp
Eventual costs of Brenkert ownership are less. So begin NOW to have that quality, that complete satisfaction, economy and pro jection efficiency that Brenkert gives you. Ask the dependable and capable Brenkert dealer to inform you fully.
BRENKERT LIGHT PROJECTION CO
ENGINEERS AND MANUFACTURERS
DETROIT, MICHIGAN, U S. A.
FEB -4 1938,
INTERNATIONAL PROJECTIONIST
VOLUME XIII
NUMBER 1
JANUARY 1938
Outline of the Requisites For A Competent Projectionist
By A. C. SCHROEDER
MEMBER, PROJECTIONIST UNION 150, LOS ANGELES, CALIFORNIA
WE OFTEN hear that it requires little knowledge and training, or both, to be a projectionist. Any- one can learn in short order to "thread a projector and push carbons into a lamp" — but does this make a projection- ist? There is so much more to projec- tion that probably none of us knows all about it.
Projection embraces electricity, me- chanics, optics, sound, mathematics, lubrication, the ability to manipulate controls at the right time and showman- ship. Some of us have a passing acquaintance with all these subjects, but the majority of us have a fair knowledge of only a few.
It might be argued that a man who can manipulate controls and who pos- sesses showmanship can run as good a show as anyone else. I wonder. I know of theatres which are indifferent to cap- able projectionists; they want button- pushers. I have never seen shows in these houses during which the picture was not discolored. Is this just a coin-
Many readers will applaud, many disagree with, this provocative contribution by a noted projec- tion craftsman. Here is provided a fine springboard for those not afraid to take the plunge into the pool of opinionated comment — and incidentally contribute to a most interesting forum on pro- jection practice.
cidence, or otherwise? The equipment is not at fault, because they operate dif- ferent lamps with unvarying results.
There have been other instances in- dicative of incapable projectionists — one being a twenty-minute stop which should have been corrected in two minutes. This particular trouble required just a bit more knowledge than the projection- ist had. Another house had a twenty- five minute "intermission" due to sound outage, caused by a blown fuse : the boys simply waited until the serviceman ar-
[9]
rived. Another instance was a faulty switch in the exciter lamp circuit, which could not be located, so the boys ran one machine until they received help.
Such troubles should not require servicemen. The exciter lamp trouble was as simple as the switch in the ma- chine motor circuit, yet the boys were stumped because it was in the sound sys- tem. A little more knowledge than these men had would be a definite asset — to themselves, to the craft.
What should the projectionist know about electricity? In this, as in other subjects listed, each man must decide for himself. I believe that he should know all that he can learn. What must the projectionist know about electricity? Apparently nothing, today; but will it still be so ten years from now? Younger men are entering the craft who know more about electricity, and the other subjects, too. Many older men prob- ably excell only in showmanship. One acquires this ability over a number of years. The newcomer cannot learn it
10
INTERNATIONAL PROJECTIONIST
January 1938
immediately. Much of the other stuff he learns in high school before he ever sees a projection room, knowledge which many men who have been operating for years have never acquired.
Projectionists' knowledge of electricity differs from that of wiremen. There is no need to know about pulling wires, or otherwise doing a workmanlike job of wiring. A great many electricians are not proficient at trouble-shooting. Pro- jectionists should be proficient thereat, but most of them are not. It is seldom necessary to "ring out" a circuit, but could you do it in an emergency? Could you find the trouble if the circuit rings out OK, yet you get only a spark at the arc? It would be embarrassing to enlist aid on such a simple problem.
Ohm's Law a Definite 'Must'
Knowledge of the electron theory is not necessary but those who know about it have little difficulty solving such prob- lems. A thorough understanding of Ohms Law is invaluable. If you do not have to stop and think before applying it, you have mastered the first big step. You cannot master electricity until you do thoroughly understand Ohms Law. It enables you to immediately interpret test lamp or meter procedure, or why a battery and buzzer will not test through a circuit where the same battery and a headset will, etc.
The mechanics section includes plenty, and some knowledge of the machinist's trade helps. A real machinist would ordinarily not have much to do in the projection room, but he would be very helpful on special occasions. The pro- jectionist should know about the differ- ent kinds of fits between a shaft and its bearings. A slow-moving, heavily-loaded shaft of large dimensions requires a far different fit than does a small high-speed spindle. There is also the temperature to be considered. One should know that a bearing may be too large for the shaft, yet, due to misalignment of two bear- ings, may seem too snug. An example is the two bearings for the intermittent shaft, which may be out of line, caus- ing the shaft to bind, or at least to be too tight. There are other causes for a shaft to bind, the key to which is a knowledge of the machinist's trade.
Many projectionists know that dowel pins hold adjoining parts in alignment, but they do not realize that a sharp blow with a hammer causes the dowels to give: the parts shift slightly and so cause trouble. It is sometimes neces- sary to file a surface perfectly flat; or, if unable to do this, to employ a trick that produces the flat surface without filing. Then we should know how to determine if the surface is flat.
Do you know that it is impossible to drill a true round hole? Some projec-
tionists purchase lathes which help them in their work. They discover, however, that it isn't a case of just sticking metal in the machine and putting it to work, but that it requires practice and experi- ence before good work results.
What do we know about optics? Not much. What must we know about optics? Again the answer is nothing. It is a funny condition when we can handle such a complicated business as projec- tion and still get by knowing so little about it. We have a source of light, the arc; but how many know how the light gets to the screen to form the pic- ture? When the light reaches the sur- face of the condenser the rays are re- fracted or reflected. When using a mirror the refraction is of no impor- tance; but with condensers it causes the light to concentrate at the aperture.
When the light reaches the objective lens it is refracted in varying degrees. White light consists of colored light, and some colors are refracted more than others. If this condition were not cor-
relatively soft: many metals and even dust particles easily scratch it, indicat- ing that careful cleaning is necessary. A lens scratch will throw light rays in wrong directions, causing loss of light and reduction in the sharpness of focus. If the lens surface is very dusty, dust it lightly with a very soft brush and then clean it with lens tissue. Sometimes silk or chamois skin is recommended, but some authorities assert that silk has very hard fibres which cause fine scratches. Chamois may have dust or grit em- bedded in it. Lens tissue is the safest.
Small air bubbles in a lens do no harm, causing only a small light loss and indicating that good optical glass was used. A lens with many bubbles is not desirable, but one or two small bubbles do no harm.
If projectionists understood the nature of sound, they would be able to grasp the servicing of the equipment more readily. By sound we mean just that — what we hear. There is no sound in the amplifiers or on the film. A study
Projection Today
r|1HE motion picture projector is no longer a mere mechanical contrivance, cranked by hand or made to operate by the simple closing of a switch. The projectionist of today must have an excellent knowledge of mechanics, electricity and optics, and is in charge of a delicate and complicated mechan- ism made with scientific accuracy to handle a fragile and inflammable material.
The projectionist has a great responsibility, for a failure to measure up to the right standards means that all that the producer, director, actor and cinematographer have striven for loses much of its artistic and com- mercial value, the pleasure of the audience is lessened, the exhibitor is sub- jected to constant and unnecessary expense, and lives and property are
endangered.
Copyright by International Projector Corporation
rected, two dots, one red and the other blue, occupying certain relative positions on the film, would not be projected to the corresponding positions on the screen. Use is made of the different refractive powers of the various kinds of glass, and when these are used in certain combinations they have the prop- erty of cancelling these faults, and the two dissimilar dots are projected to the proper points on the screen.
Care of Lenses, Mirrors
An uncorrected lens projects an im- perfect image even when the film is not. colored. If the film had a white dot and the rest of it were black, the picture on the screen would be a white dot surrounded by a colored fringe. The white center is where all the colors over- lap (white consists of all colors) ; the colored fringe is where only some of the colors overlap.
We think of glass as an extremely hard substance, but actually it is
of sound shows us what occurs when a microphone is spoken into or when a loudspeaker reproduces that sound.
Theatre acoustics is nothing for the projectionist to worry about at present.
Acoustics still is an involved subject, but there is much that the layman can learn. In the auditorium sound is re- flected, absorbed, or transmitted when it strikes a surface, depending upon the nature of the surface. Probably all three occur, but in varying degrees. As vari- ous kinds of glass react differently on different colors of light, so do differ- ent materials cause various results when high or low sound frequencies strike them. One material reflects 10 per cent of a certain low frequency, and only 3 per cent of a particular high frequency. Another material may reflect the same amount of that low frequency, but pos- sibly only 1 per cent of the high fre- quency. In this manner the acoustic engineer can treat an auditorium to im-
January 1938
INTERNATIONAL PROJECTIONIST
11
Waikiki Theatre wins Thousands with
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Your movie sound can equal the sound enjoyed by patrons of the Wai- kiki Theatre and over 4, 000 other mo- tion picture houses. Install the Magic Voice of the Screen! Equipment for small theatres or large— at a price you can pay — is available. Remem- ber—better sound means better box office— and you get both with RCA Photophone' s superior equipment.
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12
INTERNATIONAL PROJECTIONIST
January 1938
HEM COMING
As in every other business, progress in the motion picture industry means more for the same money. The only way to hold patronage is by continuous improvement of the product you are selling.
Color is an example. Patrons will de- mand more and more of it. But good color projection means high intensity snow white light.
With High Intensity projection already installed in approximately one third of the country's leading motion picture houses, with a majority of the total seating capac- ity, patrons are accustomed to modern high grade projection. They expect it everywhere.
And why shouldn't they have it? Sim- plified High Intensity projection is not a luxury. It actually costs less per light unit on the screen than old style low intensity. Because this is so, you can have two to three times as much light on the screen and cover its cost with one more admis- sion per show. Write for new, free, illus- trated booklet, "The Eternal Triangle in Picture Projection.''''
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General Offices: 30 East 42nd Street, New York, N. Y. BRiHCH SALES OFFICES: HEW YOBK PITTSBURGH CHICAGO Sill FRDfCISCO
January 1938
INTERNATIONAL PROJECTIONIST
13
prove the reproduction of sound film.
The angles of the various surfaces in the house also influence the final result. Large flat or curved surfaces sometimes cause trouble, and must be broken up, or some material capable of absorbing most of the sound must be used. On the other hand, a rough surface might be used to disperse the sound in all di- rections and thus overcome the effects ot the even smooth surface.
The projectionist should know mathe- matics (doesn't he have to figure his pay check?). The simplest problems occur in figuring the running time of the show, schedules, etc. Then we have the length of carbons required for various reels. Many of the boys have reduced these to a number of tables, one for the run- ning time in minutes starting with 90 feet and continuing up to about 12,510 feet. Another for carbon lengths, allow- ing so many hundred feet for each inch of positive and a different figure for each inch of negative.
We used to calculate the size of lens needed under given conditions, but now we use tables, and it is only the new- comer who remembers the formula. How much math the projectionist needs is again dependent on the individual. Some cannot get enough, others are satisfied with very little.
Some knowledge of lubrication is a good thing. How much oil to use is a question, so we use enough to assure proper lubrication, thus most of us use too much. What oil to use is also a problem, occasioning much discussion. It is conceded that mineral oil should be used, but there is little agreement about the correct viscosity. The lighter oils are more highly refined than the heavier ones, thus are better. The heavier auto- mobile oils (often used when projection- ists desire a heavy oil) are originally light, then a filler is added to give it more body. This filler is an adulterant, nol a lubricant. The heavier oils cause more drag, making the machines run harder.
Many projectionists think that a heavy oil is needed when the load on the shaft is high, but a light oil will support prac- tically the same weight per square inch as the heavy oil. Beyond a certain pressure per square inch the oil film fails, and we have metal-to-metal con- tact, which quickly ruins the surfaces.
Advance Planning, Showmanship
There should be no acid, dirt, or other foreign matter in the oil. Not all oil is free of acid, and some of the widely advertised oils are said to be diluted with kerosene. Acid and dirt are harm- ful, kerosene probably does no harm, but neither does it help. I prefer a white dynamo oil, light and of good quality; if bought in fairly large quantities it is
cheaper than the usual run of oils bought in small bottles or cans, and it is better.
A button-pusher may sound funny as a phrase, but it is not funny when done incorrectly. The expression, of course, refers to dimmer handles, foot switches, etc. In a new situation I find it helpful to think out the sequence of operations beforehand; there is no time to do this at the moment of making the change. I have seen experiencd men "miss" through neglect of this simple process. This may not be necessary for everyone, but it will help the majority.
Showmanship is the quality of know- ing what or how things should or should not happen during the show. As an illustration, let us consider trailers. A man should instinctively know that it is poor practice to open or close the show with the announcements for next week. There are times when different parts of the show should follow each other rapidly and without a break. At other times, a picture with a tragic ending is more impressive and the patrons receive less mental jar if a few seconds elapse before starting the next subject, especially if it be a comedy.
Even if an intermission follow the sad
ending, it might be advisable to allow the house to remain in darkness a few seconds and then bring up the lights slowly. On the other hand, if a comedy finish with a lot of laughter, it is just as well to immediately light up the house with the audience still laughing.
Projectionists do not agree on all phases of showmanship, but neither do the managers. Some people acquire this trait rapidly; others seem never to learn it. Some people instinctively do the right thing at the right time, while others do everything wrong.
Newcomers Are Better Fitted
The foregoing is the writer's idea of what a projectionist should know. It covers a lot of ground, and projection- ists have all sorts of ideas on the sub- ject. One thing is certain, the youngei men are better educated in more of the subjects than the oldtimers. As time goes on projectionists as a whole should be more capable. The newcomers make every effort to learn all they can about the business, but after a few years most of them get into the same mental atti- tude that the older men have, and learn- ing either ceases or diminishes greatly.
S. M. P. E. Discussion of Stereoscopic Pictures
UTILIZATION of advance proofs by I. P. in order to bring to its readers promptly important S. M. P. E. papers usually means that publication of the discussion incident to a given presenta- tion must be postponed. While such instalment publication is not adaptable to all technical papers, it is entirely feasible with presentations such as that anent three-dimensional motion pictures, employing Polaroid analyzers, previ- ously published herein.1
Appended hereto are excerpts from the discussion which followed presenta- tion of this particular paper at the most recent S. M. P. E. Convention:
Mr. Bradley: What is going to be done about eye-strain in using these glasses?
Mr. Wheelwright: The pictures we showed were taken by an amateur and were not perfectly projected. There is no reason why there should be any eye-strain, but there are a number of reasons why in photographing or in projecting, differences in image size can be mistakenly or inten- tionally produced. Also, individual glasses may show imperfections.
Mr. Bradley: If the glasses were made according to prescription by a skilled optometrist, could that be overcome?
Mr. Wheelwright: Yes, entirely. Polaroid is being worn in front of the eyes now for hours and hours on end, with no noticeable eye-strain when properly mounted. There is nothing inherent in polarization that would lead to eye-strain that we can discover.
^'Stereoscopic Motion Pictures: Past, Present and Future," by G. W. Wheelwright, I. P. for Nov., 1937, p. 15.
Mr. Richardson: What is the effect, if any, of distance from the viewing screen?
Mr. Wheelwright: We have to be care- ful about foreground objects and back- ground objects. We must also consider the permissible viewing area. With a 16- mm. projector and 16-mm. film area, we are straining matters in showing the pic- tures to 200 persons. With 35-mm. film the permissible viewing area is larger. Actually, there is only one very small area where everything is exactly accurate, but there is a large area in which things are what might be termed permissibly accurate. Frankly, that area has yet to be determined.
Mr. Edwards: Is it not possible that apparent eye-strain is caused by having one glass adjusted horizontally and the other vertically?
Mr. Wheelwright: There is no reason why polarization in different planes should cause eye-strain. If one were viewing re- flected glare, where polarization is a func- tion of the angle at which the glass is set, there would be a very definite reason lor eye-strain. Here the two pictures are of the same brilliancy, and the glasses are supposed to be crossed properly. Professor Kennedy has had glasses made according to his prescription, and has worked for periods of eight and ten hours doing nothing but viewing pictures without eye- strain.
Mr. Finn: The proportion of those who experienced strain seems to be about the same in the fore part of the room as in the rear. I seemed to detect certain lapses of registration, and it occurs to me that such (Continued on page 31)
c* . xt *• An important change in the
Contest Notice: mles a^plyin? to tne Awards
Contest based on the special series of articles by Aaron Nadell is dictated by experience with the first group of answers. The time limit of 20 days originally established for receipt of Contest answers in the offices of I. P. has been found to restrict un- duly those readers far removed from publication headquarters; also, the large number of answers which reached I. P. either on or after the deadline date testified to the urgent need for an extension of the time limit.
In the future, therefore, the deadline for Contest answers will be on the first day of each month, rep- resenting an extension of ten days time. This change
in Contest rules, while necessitating the omission of prize-winning names from this issue, undoubtedly will result in a more widespread interest in the Contest. Some 219 contestants have submitted an- swers to last month's questions as these lines are written (some from England, South America, and the Canal Zone), and the winners (with photos, we hope) and their prizes will be announced next month.
Meanwhile there is appended hereto the second Contest article, for the best answers to which an- other fine assortment of prizes will be awarded, including meters, test sets, tool kits, and other valu- able projection accessories. — Editor.
Analyses of Modern Theatre Sound Reproducing Units
II. Amplifiers
ALL amplifiers are trigger-operated devices, working on a supply of smooth d.c. The fact that seem- ingly only a.c. enters the amplifier, often the case, makes no difference. Such amplifiers include internal provisions for converting a part of the a.c. to the smooth d.c. The amplifier, we may say, "corrugates" the smooth d.c. supply, making of it a pulsating d.c. in which the pulsations occur at speech frequen- cies. The pulsating d.c. thus obtained is usually further converted to a.c. of the same speech frequencies.
In this work the amplifier uses a model or guide provided by the a.c. or pulsat- ing d.c. speech input, which in turn is derived from the photo-electric cell or from the output of another amplifier. It is this speech input that operates the "trigger." A good amplifier works with such precision that its output or dupli- cate speech power is an exact reproduc- tion of the "trigger" input, only stronger. In some cases the output is not actually power, but only voltage, accompanied by no appreciable flow of current — in which case the device is called a "voltage am- plifier."
The use of a voltage amplifier lies in this: frequently the controlling input, which operates the "trigger," does not have to carry any power to speak of. The trigger works, as will be seen, on voltage alone applied to what is, elec- trically speaking, a condenser of very low capacitance. A large change in the voltage, or charge, of that condenser can
By AARON NADELL
be achieved (because of its low capaci- tance) by an extremely small flow of current — so little that the current is commonly regarded as almost zero, and is seldom considered.
For practical purposes it is entirely in order to think of the voltage as acting alone, and the power as substantially non-existent. Thus, when the only func- tion of an amplifier is to provide speech input for another and larger amplifier, a voltage output alone may be sufficient.
However, when the amplifier is used to operate any device that does work, such as a loudspeaker, power is obviously needed, and a mere voltage output will not serve. Also, when an amplifier is to be used to supply input for another am-
-PLATE
HEATER Triode Type Tube
plifier of the Class B or Class AB kind, voltage alone again will fail to serve. In Class B and Class AB amplifiers the trigger needs more than voltage to make it function effectively.
Tube is the Real Amplifier
Essentially (with an exception to be noted) the only amplification that ever occurs — the only trigger action, at least — takes place in the tube. No matter how bulky the apparatus may be, the comparatively small tubes do all the real
[14]
work; the rest of the material is there only to help the tubes — to lead input to them and take output away, to bring up the smooth d.c. which the tube moulds to pattern, etc.
Most theatre amplifiers today contain "power packs" which provide the neces- sary d.c. out of a line a.c. input. These circuits, however, are properly classified under power supplies, and play no in- herent part in the amplifier action. They are excluded from the present discus- sion.
An amplifier consists, then, of sockets, or means for mounting tubes, and for connecting the necessary circuits to them. Then of wiring that applies the necessary d.c- — plate d.c. — across each tube. Since tubes need a filament-heating current, another circuit applies that current to the sockets. Still other circuits bring up one or more grid bias voltages. All these auxiliary supplies must be of cor- rect value as to both voltage and cur- rent, but there are no important ques- tions of impedance match.
The speech input and output to the tubes must, however, maintain proper impedance relations with the tube itself. The correct relationship is not always an equal match. Best results may, in this case, be obtained when the tube output works into twice its own impedance; or other output impedance relations may obtain, depending upon the nature of the tube and the circuit. Input imped- ance is usually matched to some extent, but since the input impedance of a Class A amplifying tube is practically infinite, the usual procedure is to draw that in-
January 1938
INTERNATIONAL PROJECTIONIST
15
MONOGRAPH'S MIRROPHONIC
HEAVY DUTY SOUND HEAD
• • ••
J3t
MOTIOGRAPH MlltltOPHOSIC
SOUND PROJECTION
the Result of Three Great Forces
* Bell Laboratories Research
* E. R. P. I. Engineering
■k Motiograph Craftsmanship
Contains three moving parts. Factory calibrated by Motiograph' s Master Craftsmen, it will run smoothly for years without flutter, and quietly and dependably without adjustment.
Motiograph' s Mirrophonic Sound Head is of the positive pro- pulsion type. Shafts, gears and rollers are of steel, hardened and ground. The drive shaft is lVs" in diameter . . . 60% oversize for safety. The 34-pound stabilizer insures constant film speed past the scanning beam.
Motiograph' s Optical System employs a cylindrical lens instead of a mechanical slit ... a mechanical slit masks off the light whereas with the Motiograph cylindrical lens the light slit is formed opti- cally and there is no wasted light.
The Scanning Sysiem, Exciter Lamp, Photo-Cell, Film Control unit assembly, and all other critical elements are cushioned in durable rubber, removing every trace of mechanical noise pick-up.
MOTIOGRAPH S "V" DRIVE MOTOR
Motiograph' s "V" Drive Motor is mounted in the 465-pound base and not on the sound head. This construction does three things:
1. Eliminates flutter caused by vibration from unbalanced driving power application.
2. Eliminates the possibility of motor noise being picked- up by the sound system.
3. Eliminates vibration being transmitted to Projection Head . . . one of the major causes of an unsteady picture.
Exclusive to Motiograph' s Mirrophonic Sound Head is a specially designed split drive pulley by means of which speed variations up to fifteen per cent may be compensated. This feature is essential on installations where line voltages are either above or below normal.
Without Motiograph' s positive "V" belt drive and easily adjusted pulley, it is difficult to set and maintain constant speed.
MOTIOGRAP
In c
CHICAGO, IT. S. A.
16 INTERNATIONAL PROJECTIONIST January 1938
BALANCED
IN EASTMAN Super X Panchromatic Neg- ative the vital film factors of fine grain, high speed, and superb photographic qual- ity are combined to give the finest results to be seen anywhere today. It is the admi- rable balance of these qualities that has made Super X the world's most widely used negative film. Eastman Kodak Co., Rochester, N. Y. (J. E. Brulatour, Inc., Dis- tributors, Fort Lee, Chicago, Hollywood.)
EASTMAN SUPER X
PANCHROMATIC NEGATIVE
January 1938
INTERNATIONAL PROJECTIONIST
17
put from a source of several hundred thousand ohms.
Inter-tube coupling refers to the means used for taking the speech output of one tube and applying it to the "trigger," or input, of another tube for further am- plification. Since the output of a tube
PLATE
GRID
HEATER Tetrode Type Tube
is a few thousand ohms, and the input should be hundreds of thousands or a million ohms, transformers are often used for coupling having relatively low im- pedance primaries and high impedance secondaries. Such transformers consti- tute the only exception to the foregoing statement that tubes do all the ampli- fying.
A Class A tube needs only voltage in- put to work its grid or trigger (cur- rent is of no importance) hence the coupling transformer may be given a volt- age step-up ratio, the effect of which is greater amplification. The benefit is not very striking, because transformer dis- tortion results if the step-up ratio ex- ceeds a very small increase, and many theatres use no coupling transformers. The plate of one tube is properly loaded with a resistor of a few thousand ohms value; a pair of condensers, or a con- denser and common return, link that re- sistor to one of several hundred thousand ohms, and the latter in turn constitutes the source of input for the next tube.
The high value of the input resistor is of definite benefit in promoting ampli- fication in any tube that works on volt- age only. Thus, the output of a p.e. cell may be only microampere; but if that current completes its circuit through a resistor of one megohm, the voltage drop across the resistor will be one volt — enough to work the grid of a small tube very satisfactorily, while the power is only one microwatt.
Tube Construction Data
Tubes are sensitive devices in which the current value of a d.c. circuit is controlled by voltage input that requires, in Class A operation, very nearly zero power. This sensitivity is achieved by compelling the d.c. in question to leave its metal conductors and travel for a short distance through a vacuum, wherein it passes through the meshes of a metal screen, to which the controlling voltage is applied. Under these circumstances tho d.c. value is extremely sensitive to the extent of the charge, or voltage, of the metal screen, and small changes in that voltage will cause comparatively
large changes in the strength of the vacuum current.
The current is emitted, or projected, into the vacuum by the simple process of heating the end of one of the con- ductors. Every conductor, under all cir- cumstances, constantly loses, sheds, emits small quantities of current (small num- bers of electrons) into its surroundings. This is true even when the conductor is not supplied with electricity — the elec- trons come from its own material. The property of giving off electrons easily is what makes a conductor conduct. When a group of electrons, constituting a cur- rent, enter a conductor they shove ahead of them the easily detachable electrons of the conductor's material, themselves taking the vacant places until shoved ahead in turn by additional current entering after them.
Now, all materials that are not at abso- lute zero of temperature (273 degrees below Centigrade zero) are in continuous internal agitation, the energy for which is supplied by the surrounding heat. If the electrons of the substance are readily detachable, the agitation shakes some of them loose from their moorings. Those that happen to be detached close to the surface of the material may continue right through that surface and out into the surrounding space. If the substance is heated, the internal agitation increases in intensity, and the emission may be increased to the point of releasing enough electrons to constitute a sizeable current. Some conductors emit much more easily than others, for a given tem- perature; the emitting conductor, or cathode, in a vacuum tube is made of materials that are exceptionally efficient in this way.
The necessary heat is applied by means of a heater (or filament) current, supplied to the tube for that specific purpose. The emitting material may be coated upon, but insulated from, the heating wire, or filament. On the other hand, the filament itself may be made of a metal which is a good emitter, and does double duty as a cathode, in which
7 CTT7 O
DIRECTLY-HEATED CATHODES (FILAMENT TYPE)
case it will carry two separate currents, the vacuum d.c. and the heating cur- rent, which latter may be either d.c. or a.c. Where the heating wire and the emitter
are insulated from each other, the tube is called a heater tube. Where the fila- ment performs a double duty and carries two separate currents, the tube is said to be a filament type. Both types may be found in the same amplifier.
Electron emission into a vacuum is
PLATE
SCREEN
SUPPRESSOR GRID
CATHODE
HEATER. Pentode Type Tube
not enough. Electrons are all negative; an accumulation of electrons constitutes a negative charge ; absence of the normal quantity t>f electrons amounts to a posi- tive charge. The emitter, having lost electrons, is positively charged, and will re-attract them unless a stronger positive charge is provided in the immediate vicinity.
The other terminal of the vacuum cur- rent, the anode, is positively charged from the d.c. source of the vacuum cur- rent and attracts the emitted electrons to itself. They return to the emitter through the external circuit; thus the process can keep up indefinitely as long as an external source of d.c. potential is applied to the tube to furnish the necessary energy to keep the electrons- moving around, back to the emitter, and around again.
With such external potential applied, the value of the vacuum current will de- pend in part upon the anode voltage, since there are two opposite forces at work on each electron. The cathode which it has just left, although usually considered as negative (which it is by comparison with the anode) is neverthe- less positive compared with the electron itself, and attracts it. The anode is positive compared with both electron and cathode.
An electron halfway between the two will be drawn to the anode, which is
a*
■•-CATHODE
tNDIRECTLY-HEATED CATHODES (HEATER TYPE)
the stronger charge. But at a point close to the emitter the weaker but nearer charge may predominate, and an elec- tron at that point may return whence it came, reducing the vacuum or space
18
INTERNATIONAL PROJECTIONIST
January 1938
current by just so much. The greater the positive charge of the anode, the better its chance of attracting those electrons which are emitted with low velocity and therefore do not travel very far from the cathode.
Since the vacuum is in series with the external anode or plate circuit, all elec- trons that cross the vacuum must com- plete their return to the emitter through the plate wiring, and a meter in series with that wiring will accurately read the vacuum current. An increase in plate voltage shows a proportionate increase in vacuum current, up to the limits of the emitting power of the cathode- — the vacuum in this respect obeying Ohm's Law like any other conductor.
However, the plate current can be in- creased without increasing the plate voltage merely by facilitating emission --that is, by raising the emitter to a
The grid of a simple amplifying tube is placed between the cathode and the anode. Cathode and anode are the two poles of the vacuum, or output, circuit. Cathode and grid are the two poles of the input, or control, circuit. In Class A operation a permanent d.c. charge is connected across grid and cathode in such polarity that the grid is the more negative of the two, thus negative elec- trons do not touch it and there is no flow of grid current. Because there is no such flow the grid bias may be ap- plied through the input resistor of hun- dreds of thousands or millions of ohms. The presence of the resistor has no effect at all on the d.c. grid bias because there is no grid current. Similarly, grid bias can be obtained from very small dry cells (C batteries) which never wear out except through internal deterioration.
While electrons do not touch the grid,
Noteworthy, however, is that there is some small flow of actual charge-dis- charge current along the grid wires. The electron accumulation at the grid, the charge, can be changed only by moving electrons on or off, and that motion of electrons constitutes a current. It is, however, an extremely feeble current. Grid and cathode, between them, con- stitute a condenser, and the num- ber of electrons needed to change the condenser to a given voltage de- pends upon its capacitance. The capacitance being very small, compara- tively few electrons are needed. Simi- larly, in the case of the permanent d.c. bias there is a temporary flow of elec- trons to the grid when the switch is first turned on. These must pass through the high resistance of the grid resistor, a process requiring a short time. The charge once established, however, does
RP WH
higher temperature through an increase of the heating current. The effect is the same as reducing the resistance at the emission end of the circuit. Ohm's Law still holds good.
The resistance of the vacuum itself can be reduced by the introduction of very small quantities of gas. Bombardment of the gas atoms by moving electrons de- taches other electrons from the gas, leav- ing the atoms positively charged. The positive atoms, now called ions, move to the negative terminal, or cathode, where their attraction helps to increase emis- sion. They capture emitted electrons, only to lose them again by further bom- bardment, and again become positive, and again stimulate emission. The re- sult is an increase in plate current with no increase in the applied plate voltage, or, effectively, a decline in the vacuum resistance resulting from the gas content. Ohm's Law still holds good.
they are strongly influenced by it. An electron moving outward from the emitter is attracted by the positive anode and simultaneously repelled by the negative grid. If the grid repulsion is too strong, they return to the positive (compara- tively) cathode. If the grid repulsion weakens, some of them slip through the meshes and go on to the anode. If the grid bias is set at a medium value, a small change in grid voltage may send multitudes of electrons back whence they came, or (if the change is of reverse polarity) admit multitudes to the anode that otherwise would never get there.
The input current to be amplified is merely applied between grid and cathode as a pulsating or alternating charge that modifies the grid bias. Charge, or volt- tage, is all that is needed. The com- paratively strong plate current is moulded into an exact duplicate of the grid pulsations.
••&
0
A
STPS^-
J3
T3
2
D2
U}SV-il5V;50~60~AC POWZR SUPPL*
not change, and the resistor has no further influence on it.
Many tubes have more than one grid. A very new type is the co-planar tube in which two separate grids are orig- inally so wound around the same form that they occupy the same location, or plane, within the tube, although in- sulated from each other. Each has an equal effect on the electron flow. Each is supplied with its own output, or trigger voltage, the sources of which are entirely different. Such tubes are
January 1938
INTERNATIONAL PROJECTIONIST
19
used in reverse feedback circuits that minimize distortion.!
More common is the screen grid, posi- tioned between the control grid and the anode. Its function is to overcome cer- tain limitations upon amplification in- herent in the simpler three-element tube, or triode. In the latter, a reduction in grid voltage, originating with speech signal, results, as explained, in an in- crease in plate current. But, the source of plate voltage not being of infinite capacity, increased flow of plate current tends to reduce the plate's positive charge.
Inherent Tube Fluctuations .
Now, plate and grid constitute a con- denser. It has been said that an electric charge can no more exist without an equal but opposite charge existing somewhere else than a board can have only one side. If the plate voltage drops a little, the grid voltage must rise a little. But the grid voltage increase re- duces the plate current again, causing the plate voltage to rise, which by the same condenser action again reduces the grid charge. In other words, there are small fluctuations inherent in the tube action, independent of the pattern of the input. Carried far enough, these fluctua- tions will make the tube develop an a.c. on its own account, that is, act as an oscillator. When things go that far,
tNOTE: Reverse feedback was explained in I. P. for Nov., 1937, "The W. E. 91-A Amplifier," p. 19. A co-planar tube may be used in place of V-l in the 91-A amplifier, schematic of which accompanies this month's article.
Here are the Contest Questions—
5. The plate current meter of a given tube reads high. The plate volt- age and all other voltages of the tube are approximately normal. What is wrong? What should be done to cor- rect the condition?
6. Dirt in a socket results in open contact at the grid of a Class A tube. What result can be expected? Will sound be lost?
7. A short-circuit in or about a screen-grid resistor effectively connects the screen-grid with the plate. What will happen?
8. An internal tube defect short- circuits the filament to the control grid. What will happen in Class A amplifica- tion? In Class B? In Class AB?
the only sound heard is a continuous squeal, howl or whistle, depending on the frequency of the a.c. generated.
Many theatres have a slight, high- pitched hum in the background of their sound, normally unnoticed, which is due to a slight degree of oscillation on the part of the amplifying tubes. In others, the oscillation is above audible fre- quency, but is heard through its inter- action with the audible sound as distor- tion. Good amplifiers in good adjust- ment do not oscillate. The greater the amplification, however, the greater the tendency of the tube to oscillate.
High amplification without oscillation
is promoted by reducing the condenser coupling between plate and control grid. A screen grid is placed between them for this purpose. It is positively charged, al somewhat lower voltage than the plate charge, and attracts some electrons. Most electrons, however, on reaching the vicinity of the screen grid are drawn further on by the still more powerful plate attraction, and pass through the screen meshes.
Suppressor Grid Effect
This construction makes possible higher amplification without oscillation, but in itself does not secure high amplifica- tion. Oscillation having been eliminated, secondary emission remains to be over- come. Many projectionists have seen tubes with plates so hot that they glowed a cherry red. The cause is bombard- ment by the vacuum electrons. But hot conductors, even when not made of emit- ting material, emit considerable quan- tities of electrons. When the plate is heated to the point of substantial emis- sion, the electrons leaving it have no place to go — the plate being the most positive unit in the tube, they go back where they came from. Temporarily, however, each electron constitutes a little negative charge in front of the plate, which tends to repel the vacuum current coming from the cathode. Hence, the value of the vacuum current, and there- fore the possible extent of amplification, are reduced.
This effect is overcome by introduction of a suppressor grid between the screen (Continued on page 29)
Boston Local 182 Model Admittance Procedure Is Fair, Thorough and Efficient; Long Used
HIGHLIGHTING Boston Local 182 system of handling membership ap- plications is group examination in writ- ing of oral questions, as shown in accompanying photograph. First requi- site for applicant is that he live within 182 jurisdiction and have had a pro- jectionist license for two years preced- ing.
Next step is the appointment by the chair on the open floor of a meeting of an investigating committee composed of five men for each applicant. Any member has the right to challenge any appointment to investigating committee, thus insuring a fair shake for every applicant. Investigating committee then reports back to the body, which can accept or reject recommendations. If investigating report is accepted, ar- rangements are made for thorough ex- amination of applicant.
Accompanying photograph shows a group examination, all applicants pic- tured therein having been members of Local 182 apprentice class, excepting five who were included through either transfers or organizing activities. Pre- siding over the examination are the five
chairman of committees (shown stand- ing) who shoot oral questions at appli- cants, who write their answers. No questions are written down in advance by interrogators, thus insuring the ut- most secrecy. Paper of each applicant
is subsequently checked and marked by the examiners, a report of which goes back to the body for final action on ad- mission.
This is the finest procedure on Local Union admission to come to the atten- tion of I. P., and it detracts nothing from the credit due Local 182 if other local units follow a similar, or possibly even better, procedure. — J. J. F.
This is how Boston L. V. 182 conducts a group examination
20
INTERNATIONAL PROJECTIONIST
January 1938
Film Aperture Rest Decision Rests 111 With Rest of Experts
POSTING of the decision in favor of Herbert (Simplex) Griffin in the battle of split seconds anent film frame aperture rest (I. P. for Dec, p. 22), far from settling matters, in- duced a flock of responses of an ex- tremely critical nature directed not only at the referee (I. P. merely donated the arena for the battle) but also at a startled Mr. Griffin who was already sampling the fruits of victory. Some of the boys even hinted at a long count in Mr. Griffin's favor.
In brief, many of the boys good-na- turedly cuffed Mr. Jack Leatherman, of Florida, suh, who alone was adjudged by Mr. Griffin to have submitted the correct answer, (p.s. : Mr. Leatherman having already beaten us for a one- year subscription renewal for his an- swer, we're on his side. — Ed.) These two-timers, that is, those who returned to the fray after the final gong sounded, are backing Walter Fink, who insisted that a film frame rests at the aperture for only 1/30 second, as compared with the 1/48 second entry of Messrs. Griffin and Leatherman.
It would be great sport if these "operators" who "merely throw a switch" (see any exhibitor report on projectionists) could shoot a smart uppercut and straighten up Mr. Griffin, who has lived with intermittent move- ments for 25 years; but since he got us into this thing, he must get us out.
Anyhow, we present herein several representative howls from the adherents of Mr. Fink, all of which not only sub- scribe to his proposition but go to rather extreme lengths to prove the point. While the burden of all these letters is the same, each adopted dif- ferent tactics to get his message across. Mr. Gallery, of Auburn, N. Y., not only threw a verbal brickbat in the direction of Mr. Griffin but sent it winging on its way with a heavy wrapping of drawings laden with India ink and sharply- pointed indicia. The texts of these let- ters clearly indicate the point at issue, but it would be a pity to exclude the Gallery art work (Figs. 1 and 2), and the chances are that many readers will really appreciate this graphic presenta- tion of intermittent movement action.
Mr. Mowery, brother Local member of Mr. Fink, takes a different but highly effective tack by means of hav-
ing a Simplex intermittent engineer bear witness against Vice-President Griffin. (We're beginning to really en- joy this.) If this particular engineer doesn't leave suddenly on a vacation, it might be well if he and Mr. Griffin got together some afternoon in a corner of the Simplex plant and compared a few notes.
Mr. Garwin of Cleveland Local 160, while disdaining to draw any pictures, indulges himself in a select collection of sentences, which, while constituting no Vesuvius, contain enough heat to light a few cigarettes. 'Twas always thus with these Cleveland fellers. Nice playmates this fellow Fink has.
Aroused by this unexpected counter- blast, Mr. Griffin re-enters the arena and lashes out with both hands, words and a drawing (Fig. 3), the latter in particular being his idea of the retort devastating. His reply is directed speci- fically at Mr. Garwin, but since all three dissenters stand on the same proposition, the Griffin opus is inclu- sively applicable. Here are the self- explanatory comments, with Mr. Griffin being accorded the last slot:
To the Editor of I. P.
Regarding the question of the time the film is at rest at the aperture, and that consumed during the motion of the film in a Simplex mechanism, I must differ with you, and Mr. Leatherman, and even with Mr. Griffin, in your solution. I may be sticking my neck out to get into a discussion on Simplex mechanisms with Mr. Griffin, but it is my opinion that he has put his foot into it, if you get what I mean.
My analysis of the problem is as fol- lows:
At 90 ft. per minute, we are project- ing 24 frames per second. The shutter makes one complete revolution for each frame, and requires 1/24 second to do so. Further, the shutter area is divided into four 90° segments, two of which are openings, one a cut-off blade and one a balance blade. The total screen exposure occurs during the time the shutter openings uncover the aperture and is 2/4 of 1/24 second, or 1/48 second.
The cut-off blade passes in front of the aperture during x/± of a revolution of the shutter, and takes ^4 of 1/24 sec- ond, or 1/96 second to do so.
But, the film is not in motion during all of that 1/96 second. If it were,
travel-ghost would be in evidence. That 1/96 second comprises first, the time consumed by the cut-off blade's entering edge to move down across the aperture and completely cover it — during which time the film is at rest; second, the time consumed by the motion of the film, and third, the time consumed for the cut-off blade's trailing edge to move off the aperture and uncover it, during which time the film is again at rest, remaining so until the aperture is again com- pletely covered by the cut-off blade at its next revolution.
The motion required for the entering edge to just move across the aper- ture amounts to 9° of revolution; the same is required for the trailing edge to move off the aperture after film-mo- tion has ceased. The cut-off blade is a 90° segment; of that 90°, 18° is used in covering and uncovering the aper- ture, leaving 72° for the actual film- motion.
In other words, film-motion consumes 72/90 of the entire time during which the cut-off blade is in front of the aper- ture, or:
72 1 1
of , or second
90 96 120
The film is at rest during: 115 14 1
120 120
120
30
24 120 second.
I believe that Brother Fink of Local 218 is correct in his solution, and I should like to see credit given where it is due. Robert Garwin
Park Theatre, Cleveland, Ohio
To the Editor of I. P.
I cannot agree with the "Decision Rendered . . ." anent film frame aper-
A~ SPROCKET JUST STARTI1C TO TORN
FIGURE 1
Representing flywheel end of Simplex intermittent. Place a piece of cardboard in back thereof and on this trace the periphery of the wheel. Rotate flywheel very slowly until sprocket starts to move. Mark flywheel and the circle on the board as Start (A). Rotate flywheel very slowly until sprocket stops, then mark card opposite flywheel mark. Lay put angle and measure, and you get 72°. Flywheel turns once every 1/24 second, and sprocket turns in 72/360, or 1/5, of that time, or 1/120 second. (J. Gallery.)
January 1938
INTERNATIONAL PROJECTIONIST
21
ture rest, as recorded in I. P. for De- cember. I agree with Brother Fink of Local 218. I do not know how he arrived at his solution (he didn't make that very clear) but I shall try to prove that his answer is correct, i.e., that the pull-down period is 1/120 second, and not 1/96 second, and that the "period of rest" is 1/30 second, and not 1/32 second.
It is true, as stated, that the Simplex is a 90° movement, but here is the joker: some time is lost while the cam pin is entering and leaving the star slot. Actually the movement of the sprocket occurs in 72° because of this lost time.
I enclose two drawings, one of the shutter with relation to the movement of the intermittent sprocket (Fig. 1), and one of the intermittent fly-wheel with relation to the movement of the intermittent sprocket. Both show clearly (I hope) that the sprocket movement occurs in 72°, or 1/20 sec- ond, and not 90°.
Therefore, the pull-down period is
1/120 second; the period of rest is
1/30 second, and the period of exposure
is 1/45 second. James J. Gallery
Local 119, Auburn, N. Y.
To the Editor of I. P.
I vote for Brother Fink's answer . . . The intermittent, comprising of cam and pin and star-wheel assembly, is a 70°, or 4-to-l, movement, and not a 90,° or 3-to-l, movement, as stated by Mr. Griffin. Cam and pin move 72° to turn the star- wheel 90°. How would Mr. Griffin eliminate travel-ghost with a 90° shutter and intermittent? If the cut-off blade were covering the aperture before the film started to move, the aperture would be entirely exposed to light before it stopped moving ...
On a recent visit to New York, Brothers Adams, Weist and myself (also of Local 218) visited the Inter- national Projector plant. The chief engineer of the intermittent department informed us that the movement was
belat/i/e t/me and travel of //vreeM/rrew movement
T/ME ELAPSED /N THOUSANDTHS OF A SECOND
FIGURE 3 77m is the result obtained by Mr. Griffin and a corps of Simplex engineers. These data cover four factors which en- ter into the ques- tion of film frame aperture rest
|
k |
90 |
|
V |
|
|
\j |
|
|
0 |
80 |
|
s |
|
|
•o |
|
|
i |
70 |
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743 700
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IOO
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ID
SI
ROTATION IN DEGREES OF ACTUATING P/N AND ALSO OF SHUTTER FOR SAME INTERVAL
4-to-l, not 3-to-l, and verified my preceding statements. He also stated that the Powers movement was a little faster than the Simplex, being approxi- mately 4^-10-1.
International Projector Corp. has had experimental movements with a ratio as high as 8-to-l which give 35 per cent more light on the screen than does the present movement; but the film sprocket holes lasted for only three runs through the projector.
Raymond Mowery Mahanoy City, Penna.
To the Editor of I. P.
I read with a great deal of interest the letter from Robert Garwin of Cleve- land, Ohio, and I was very glad indeed to receive this letter since it shows that
FIGURE 2
STARTS
A is the leading edge of the cut-off blade The cut-off travels from A to B (9°) before
the sprocket starts to more.
The sprocket is then la motion for 72°, not 90 , and then stops, leaving 9° on the trail- ing edge to uncorer the aperture During the period of the revolution from A to B the cam pin is entering the star slot, but the sprocket is not tur^.f, vor the 9° ot the trailing edge of the cut-off blade the cam pla is leaving the star .lot.
This drawing and attendant indicia is the method utilised by Mr. Gallery to sustain his point. Compare with Fig. 3 submitted by Mr. Griffin
the boys get to thinking about somewhat intricate problems and do not hesitate to publish their ideas.
Unfortunately, however, Brother Gar- win is not quite right in his calculations, and I have had made up by our engi- neering department, after careful analy- sis, a chart showing the relative time and travel of the intermittent movement in time lapses in thousandths of a sec- ond, the rotation in degrees of the inter- mittent sprocket, the film travel in thou- sandths of an inch and the rotation in degrees of the actuating pin and also of the shutter for the same interval. This chart accompanies this statement.
My original contention still holds true, since as nearly as it is possible to de- termine, the film is moving, for all prac- tical purposes, during 1/96 second. It must be remembered, however, that all statements are made only in connection with a properly assembled and adjusted new intermittent movement.
In such a movement, the film during the first three dgrees of the pin travel moves .0007" ; in six degrees .0028" ; and in nine degrees .0069", and comes to rest in approximately the same figures. The film is moving, when the pin has entered the slot only three degrees, at a speed of 20 feet per minute, and it increases in speed up to 45 degrees ap- proximately 870 feet, or l/6th of a mile, a minute. It decelerates at the same speed.
In other words, the film speed at 45 degrees of the movement is about 43% times faster than it is when the pin has entered three degrees. Under these circumstances, I am sure we can still assume that, for all practical purposes, the film is in motion for just about l/96th of a second, and for just about 90 degrees of the movement.
Herbert Griffin
Some Television Problems
A Description for Laymen
By ARTHUR VAN DYCK
MANAGER, RCA LICENSE DEPARTMENT
This is the second and concluding instalment of this article, one of a series covering recent technical developments in television and charting the future of the art. Written by acknowledged authorities on the subject, this series should prove of great value to those interested in the progress of this baby art — as are most projectionists. These articles were compiled and are copyright by RCA Institutes, Inc. (except where another source is indicated) and appear herein through the courtesy of that organization.
n.
SO FAR, we have not considered the receiver specifically. That, to most people, is the most interesting part of the system. It seems to be the focal point of the thrill and mystery in "pictures from the air." So, let us now consider the receiver, but let us do so with clear understanding that it is only part of a system, and that it must have and maintain an intimate, accurate re- lationship to the rest of the system.
The television receiver antenna is energized by the travelling waves, which cause corresponding currents to flow from the antenna to the receiver. The receiver is tuned to the particular fre- quencies to be received in order to maximize the ones desired, and to minimize undesired ones, just as in a sound receiver. These currents, even when turned in to maximum, are very small, and are fed into vacuum tubes to be amplified. After this operation they are large enough to operate a device designed to convert them into light images.
This device is called the "Kine- scope,"* and is the inverse of the "Iconoscope"!. The "Kinescope" has a plate and a beam of electrons playing upon it, just as does the "Iconoscope." In the "Kinescope," however, the plate, or screen, is made differently; in fact, it is one end of the tube itself, made nearly flat, and coated on the inside with a very thin layer of material which has the property of flourescing, or giv- ing off bght, whenever electrons strike it. Some fluorescent materials will glow for a considerable time after being struck by electrons. The particular compound used for "Kinescopes" is chosen so that the glow dies out shortly after the electron beam moves away, and before it returns again.
The tiny electron beam in the "Kine- scope," whenever it is not moving and therefore strikes the screen in one spot,
•Trade Mark Registered U. S. Patent Office. tSee I. P. for Dec, 1937, p. 11.
causes a bright glowing spot on the screen at the point of contact. This spot is about the size of a pinhead. Although the glow is really on the in- side of the tube, it is visible on the outside because the end of the tube is clear glass, and the screen of fluorescent material is very thin.
The brightness of the spot depends upon the strength of the electron beam, and varies as the strength of the beam is varied. That spot of light is used to reproduce each spot of the picture, one at a time, by moving it around all over the picture area. It must be moved in exactly the same way that the "Iconoscope" beam at the transmitter is moved, which in modern systems is in horizontal parallel lines from top to bottom.
Beam Moves 30 Times a Sec.
So this beam will be very, very busy, too. It is going to move all over the picture in regular fashion, and repeat the travel 30 times per second. Further* more, while moving, it is going to vary in brightness continually as it "paints" the lights and shadows of each tiny ele- ment of the picture. To our slowly react- ing human eyes, the spot will not be visi- ble because it is moving so rapidly, and the screen will appear to be illuminated evenly all over the picture area; but we must remember that actually the light and the scenes are caused by one tiny spot of light flying over the screen and varying in brightness as it goes.
Much of the receiver apparatus is for controlling the movements of the beam, and feeding to it the currents which have been received from the transmitter, in order to vary the strength of the beam and therefore the brightness of the fly- ing spot. Of course there are many engineering problems associated with this apparatus. The most interesting ones are those associated with what is called "synchronization," or the neces- sity of keeping the flying beam of the "Kinescope" in perfect step with the flying beam of the "Iconoscope," even
[22].
though they may be miles apart with only a tenuous radio connection between. Obviously these two must be kept to- gether very accurately, even though they are moving very rapidly over the pic- ture. It would not do at all to have the beam at the transmitter picking up the sparkle of highlight in the eye of the beautiful television lady artist, while the receiver beam was working where her nose was supposed to be.
Method of Scanning
The object to be attained may be stated simply. It is merely that the electron beams of the "Iconoscope" and the "Kinescope" are to be kept in per- fect step with each other. Each is to travel across its plate or screen in hori- zontal lines. Each is to start at the upper left corner, let us say, move across the first or top line at the proper speed, quickly jump back to the left and start on the second line just below the first line, complete that, jump back for the third, and so on until it has covered all 441 lines, finishing at the lower right corner. Then it must jump up to the upper left corner and begin again on the top line.
Perhaps we should note here that the method of scanning actually used in modern systems does not move the spot in quite such a simple regular fashion, but has a more complex movement such as doing lines alternately, all the odd- numbered ones first, and then the even- numbered ones. This is known as "in- terlaced scanning" and provides several important technical refinements and benefits. It is not necessary to study this more complex method, however, to understand the basic fundamentals of the system, and we may assume that the beam travels over the picture from top to bottom, line after line pro- gressively.
The beams in each case are made to move by magnetic fields produced by currents in coils mounted on the sides of the "Iconoscope" and "Kinescope." If the right currents are fed into these coils at the right times, the beams will move as desired. The currents can be obtained from vacuum tubes arranged as oscillators, but one beam is at the transmitter and one is at the receiver miles away. We must have these oscil- lators working absolutely together — be- cause if they deliver their currents out of step by even as little as one one-
■
January 1938
INTERNATIONAL PROJECTIONIST
23
millionth part of a second, the repro- duced image will have no likeness to the original. So they must be tied to- gether somehow.
At present this is accomplished by making the generators of currents at the transmitter into masters of the situa- tion. They are arranged to send out short timing signals, called synchroniz- ing signals, and there are two of them, one for keeping the beams together hori- zontally, and one for keeping them to- gether vertically. These signals are additional to the picture signals, so that a television transmitter sends out three different signals, one describing the pic- ture, and two to keep the beams in step horizontally and vertically.
Of course, if they were all sent out simultaneously they would interfere with each other. Therefore the synchronizing signals are sent out very quickly during the short time intervals when the beams are not being used for the picture, but are occupied in jumping back from right to left preparatory to starting a new line of the picture. This means, in effect, that each receiver of all those which may be "looking-in," is continu- ously receiving instructions and assist- ance, from the transmitter, by means of which it is enabled to keep its "Kine- scope" picture beam exactly in step with the scanning beam at the transmitter.
Synchronization is one of the television problems which has been solved, and it is a considerable triumph that we are able to control apparatus at a distance with a precision measured in fractional millionths of a second!
Avoid Servicing Problems
A problem of receivers in process of solution is that introduced by the neces- sity of making them so that they can be operated and adjusted satisfactorily by the general public without their having to take an educational course in tele- vision engineering. The television re- ceiver is a complex instrument, far more so than present sound receivers. It in- cludes a complete sound receiver to start with, to receive the sound which accompanies the picture. Beyond that are the circuits and tubes which tune and amplify the picture signals, the cir- cuits and tubes which tune, amplify and utilize the two synchronizing signals, and the "Kinescope" tube with its associated circuits.
Many correct adjustments must be made before the picture can be viewed, and if too many of these are required of the operator, or those required are too critical, it will be impossible for the layman to operate the receiver satisfac- torily. Therefore most of the adjust- ments must be accomplished automatic- ally, and only a few left to the operator. This makes the receiver design more
difficult, of course, but the status of progress toward solution is such today tbat is is possible to promise that when television receivers are put into public use, they will be sufficiently simple in operational requirements.
A problem always noticed by the lay- man is that of size of the reproduced picture at the receiver. At present there are two standard sizes, one about 5 by 7 inches, and the other about 7 by 10 inches. Scenes of any size can be tele- vised by the transmitter merely by using the appropriate optical lens to focus them on the "Iconoscope." At the re- ceiver, the size of the picture is deter- mined definitely by the size of the screen on the "Kinescope." There is a limit of physical size beyond which it is im- practicable either to build these tubes, or to house them in cabinets of reason- able size for the home.
Most Desirable Picture Size
It seems to be general experience that the most desirable size of picture for television or motion pictures is that where the height is about one-fourth the distance between the screen and the observer. Such a size seems to give the maximum of realism or emotional ap- peal. In the home, the desirable view- ing distance is at least 8 or 10 feet, so that the picture height should preferably be at least 2 feet. There is good promise of eventual accomplishment of this goal, but at present it seems probable that the television receiver which is "just around the corner" will have a picture about 7 by 10 inches.
Often it is asked why this picture can- not be increased simply by optical means, with a lens to magnify it several times. This could be done insofar as size is concerned, but the brightness of the picture would suffer in proportion, or actually even more than in propor- tion, and the original amount of light available from the fluorescent screen is not enough to permit so much spread- ing out.
This matter is perhaps the most seri- ous problem of television, at least from the user's viewpoint; but since it is true
that the resources of Nature are infinite, and that we have only to find the way which exists somewhere, it seems definite that sooner or later even this difficult problem will be solved.
And now we have traversed the sys- tem, from the beginning where we had only imponderable light waves picked up and focussed by a camera lens, to the "Kinescope" screen, where the well-regi- mented electrons of a beam have pro- duced an image on a fluorescent screen. A summary of the major problems encountered appears to be in order and may furnish an appropriate conclusion to this discussion.
Summary of Problems
Foremost among the problems is that oi standardization. We have seen how intimately related the transmitter and receiver must be; consequently many receiver design features and many trans- mitter design features must be definitely related, and this must obtain whether the apparatus is made by one or any num- , ber of manufacturers. In sound re- ceivers, this difficulty does not exist, and any receiver built by any manufacturer readily receives any station built by any manufacturer, with very little coordina- tion. In television, many factors must be chosen, standardized, adopted, and maintained by all concerned, or the rest will be — no picture! If wrong choices were made, the art would be permanently handicapped. Therefore it has been necessary to proceed cautiously, and to make certain that decisions would stand the test of time.
The next most serious problems have been in the development of devices which would convert light to electricity and electricity back into light, in easily and accurately controllable fashion. The "Iconoscope" and the "Kinescope" have answered this need, but studies and ex- periments to improve them will continue.
The necessity of transmitting so much information in so short a time, in order to describe moving pictures electrically, has compelled the use of very high fre- quency currents and radio waves, much (Continued on page 28)
The Kine- scope, used in the RCA
television reproducing
apparatus
Projecting Hi- and Low-Range Prints; Standard Fader Setting Data
SINCE the advent of recorded sound to motion pictures there has been a continual improvement in the qual- ity of sound recording and sound re- production by extending the volume range to produce greater dramatic effect. Improvements in recording naturally re- quire improvements in reproduction. Improvements in amplifiers permit a wider volume range, and the theatre re- producing apparatus must consequently be capable of transmitting this increased range.
Some of the recent developments in reproducing equipment include: the in- troduction of new design horns which give far better quality than was formerly possible, and a more even and adequate distribution of sound throughout the theatre auditorium; improvements in the film running mechanism which have re- duced flutter to a minimum ; and in- creased amplifier power, which will ade- quately reproduce without distortion the wider power ranges now being recorded on the film.
It is recognized in the studios that until such time as all theatres are fitted with modern equipment, methods must be adopted which allow the wider vol- ume range films to be reproduced to their best advantage in those theatres having equipment capable of this re- production, but which do not penalize those theatres fitted with reproducing equipment not capable of handling the wider volume range.
Track Area Limits Output
The film received in theatres has an output limited by the dimensions of the track. The maximum volume range, i.e., the range from the faintest to the loudest sound which can be satisfactorily repro- duced, is limited by the volume range
These data, reflecting important ad- vances in the reproduction process, are promulgated by the Academy of M. P. Arts & Sciences following intensive ap- plication over a long period of time by its Committee on Standardization of Theatre Sound Projection Characteris- tics. Specifications covering fader set- ting instruction frames now become an integral part of the Standard Release Print, the indicia to appear in the space originally provided therefor.
Standard nomenclature for sound tracks will be described and illustrated in the next issue of I. P.
between surface noise and the total track sound output.
During the past year several of the major companies have, in a limited num- ber of releases, made available to the theatres two general types of prints: one type being the "Regular" release print with the ordinary volume range, and the other type, divided into two classifications according to the volume range recorded on the film, known as "Hi-Range" and "Lo-Range" prints.
The "Hi-Range" prints, requiring in- creased amplifier power in the repro- ducing equipment, and having an ap- proximate sound intensity range of 50 db, produce intensity changes which closely approximate those occurring in Nature. Musical passages so recorded and subsequently reproduced with ade- quate power, lend the added color and naturalness necessary to insure more complete enjoyment of the presenta- tion.
Those productions released on "Hi- Range" prints will also be available on "Lo-Range" prints, the volume of which may correspond with the studio "Regu-
lar" prints, or may be recorded to play 3 or 4 db above the particular studio's average. (See Figures 5 and 6). In other words, any production issued on "Regular" prints will be distributed completely on one type of print, while any production available on "Hi-Range" prints will also necessarily be available on "Lo-Range" prints as well.
As more and more theatres are con- verted to the modern equipment cap- able of reproducing wider volume ranges, the practice of issuing "Hi- Range" and "Lo-Range" prints will un- doubtedly be rapidly extended.
The success of such productions as "Maytime," "100 Men and a Girl," and other similar musical productions re- leased on "Hi-Range" prints indicate that this type of release print has a definite place in the industry from a showmanship standpoint. A complete appreciation by the exhibitor of the technique required for their reproduc- tion will insure still greater box-office success.
By means of improved technique in the studio, "Hi-Range" prints have a controlled balance of volume between dialogue and music; that is, relative re-. production between the dialogue and music has been predetermined by ex- perienced showmen after careful con- sideration of the output level.
The sound volume reaching the ear of a patron from any given print pro- jected at a certain fader setting depends upon the percentage modulation of the signal on the film. On "Regular" prints (projected at the average fader setting for any particular studio's product), both the dialogue and music are given 100% modulation a greater part of the time. This means that the output vol-
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i-LOOR AREA Or THEATER CHUN0RE0.3 OF SOUARE FT.)
FIGURE 1
Recommended amplifier output in electric watts in terms
of floor area
20 3 4 5 6 7 89100 2 3 A 5 6 7 89 1000 2 3 1 1 6 7 8 910000 •
VOLUME OF THEATER (THOUSANDS OF CUBIC FT )
FIGURE 2
Recommended amplifier output in electric watts in terms of volume
[24]
January 1938
INTERNATIONAL PROJECTIONIST
25
FIGURE 3 Recommended am- plifier output in el- ectric watts in terms of seating capacity
SEATING CAPACITY OF THEATER. (NUMBER OF SEATS >.
ume will be practically the same throughout the production.
In recording "Hi-Range" prints, however, most of the dialogue passages are intentionally reduced in modulation so that the average dialogue modulation rarely exceeds 50 per cent, while the music is recorded at 100 per cent modu- lation. This provides a volume differen- tial between music and dialogue of at least 6 db. "Hi-Range" prints do not necessarily provide louder sound, but an extended volume range which gives more dramatic value in the theatre.
When such a print is projected, the fader must be raised at least 6 db for proper dialogue volume* To utilize this volume range on the film the theatre must necessarily be provided with an amplifier output which is increased by approximately the same range. In- creased amplifier power is necessary since in the past the average theatre installation has had only sufficient power to reproduce dialogue satisfactorily. In general, those theatre installations equipped with modern loudspeaker sys- tems have sufficient amplifier power to adequately reproduce this higher volume range.
By observation of a number of houses it has been found that a theatre con- taining up to 1,000 seats requires from 10 to 15 watts of power, from either the original old standard horn systems or the more modern two-way loudspeaker systems. Houses having from 1,000 to 2,000 seats require from 19 to 24 watts of power; and theatres with over 2,000 seats require at least 48 watts.
General Power Classifications
These general classifications will serve to determine the amount of power neces- sary for theatres with seating capacities as outlined above. However, in order to demonstrate the basis upon which these rules were formulated, there is in- cluded in this report several charts. These charts indicate the theoretical minimum requirements for a theatre of any given size or seating capacity, while the information in the paragraph above
See data under heading of Setting Instruction Leader."
is based upon combinations of ampli- fier equipment actually available com- mercially at the present time.
Figure 1 shows the recommended am- plifier power output in terms of the theatre floor area; Fig. 2 in terms of the cubical contents of the theatre; Fig. 3 in terms of the number of seats in- stalled.
. These curves indicate the necessary amplifier capacity to maintain a high quality sound reproduction, but since the required power is partially dependent upon the absorption and reverberation characteristics of the theatre auditorium, deviation from these values may be re- quired, depending upon the variation of any particular theatre from optimum re- verberation conditions.
In reproducing a high-volume print, the theatre manager and projectionist should follow the usual method of set- ting the fader for proper dialogue vol-
ume, which will automatically insure a proper reproduced volume level for any musical or sound effects passages in the same production. // the volume level of the music or sound effects is reduced to a point lower than that originally in- tended at the time of the recording, dialogue passages will be too low for satisfactory reproduction.
It might be pointed out that sound recorded for motion pictures in the stu- dios today is recorded so that in general it may be projected in the theatre on one fader setting throughout the entire production. Although this is the gen- eral aim in each studio sound depart- ment, it may not be possible to project an entire production or an entire reel at one identical fader setting, due to the fact that release prints are often dam- aged and replacement sections must be inserted from time to time which may not be processed exactly as is the orig- inal print, or because there may be varia- tions in the processing of the original prints.
If the equipment is not functioning properly, or if there is insufficient power capacity, the higher volume portions of the musical passages will reproduce with harshness and distortion.
When such prints are reproduced on the older-type theatre systems, the in- crease in amplification necessary to properly reproduce the high volume passages will ' sometimes introduce ob- jectionable hum and other system noises which can usually be eliminated by care-
FIGURE 4
Specifications for Standard Release Print leader, show- ing location of stan- dard fader setting instructions. (For other data on motor and change - over cue, and reel end leader, see complete specs, for 35 mm. release prints, prev- iously published).
Protective Leader
Shall be either transparent or raw stock. When the protective leader has been reduced to a length of six feet it is to be restored to a length of eight feet
Identification Leader (Part Title)
Shall contain 24 frames in each of which is plainly printed in black letters on white background: (a) type of print, (b) reel number (Arabic numeral not less than J4 of frame height), and (c) picture title.
Synchronizing Leader
head of Starr
Shall consist of 20 fraro. including Start mark, to p In the center of the fi picture and sound trac which is superimposed
ark, then 12 feet.
opaque except as specified below:
t frame there shall be printed across the
area a white line 1/3 2 inch wide upon
diamond '/, inch high.
The
: 15 fr. inform)
nay be used by the If not so used this
[ud,<
for sensitometr shall be opaqu
The Srart mark shall be the 21st frail
START (inverted) in black letters on
Academy camera aperture height of .631
photography of this fran beginning of picture.
and all others be
. in which is printed hite background. The ch shall be used in the
From the Start mark to the picture the leader shall contain frame lines which do not cross sound track area.
In the frames in which the n words "six" and "nine" (als diately below the figure, to el ing in the projection room < inverted numerals.
als "6" and "9" appea 'erted) shall be placed te the possibility of mis o the similarity hetwee
riLM c DISC ftCCL
read- i the
Beginning 3 feet from the first fram. plainly marked by a transparent black numeral at least l/2 frame numerals shall run consecutively fr< point exactly 20 frames ahead of the frame there shall be a diamond (wl inch high by Y, inch wide.
of pit
each foot i Footage ir
me conta
height.
3 to 11. inclusi nter of each footag e on black back-jrc
'Standard Fader
26
INTERNATIONAL PROJECTIONIST
January 1938
FIGURE 5 Standard fader instruction leaders
ful adjustment or modification of the system.
The use of the higher amplifier power necessary to reproduce these prints also requires that the distribution of sound throughout the theatre be particularly uniform. In this type reproduction, flutter due to poor motion of film through the sound head, if present, will be particularly noticeable.
In order to assist projectionists, as well as the exchanges, in quickly identi- fying the "Hi-Range" and "Lo-Range," as well as "Regular" prints, each of the major studios will, effective immediately, label each print "Hi-Range" or "Lo- Range," or "Regular," and designate a general average fader setting at which the print should be projected — this in- formation to be included in the Standard Release Print Leader on each reel of each production, in accordance with specifications outlined under the suc- ceeding heading.
It is suggested that all theatre pro- jectionists carefully watch every print in order to take advantage of this addi- tional information which should assist in increasing the showmanship value of recorded sound.
S. R. P. Fader Setting Instruction Leader
TO FURTHER aid in the proper handling of "Hi-Range" prints the studios are now utilizing that part of the Standard Release Print leader which has been designated for use for any pertinent information to be transmitted from studio to theatre. A portion of the specifications for the S. R. P. leader indicating the location of this instruc-
tional information, is shown in Fig. 4, with details of the information to be known as "Standard Fader Setting In- structions" illustrated in Figs. 5 and 6.
The Standard Fader Setting Instruc- tion leader shall consist of 15 frames located as specified S. R. P. leader) in) the synchronizing leader; the first frame shall designate the type of print; the second frame the type of reproduc- ing equipment necessary to project the print; and the next nine frames the general fader setting specified in rela- tion to an average fader setting for the particular product under consideration. The remaining frames may be used for whatever additional information the studio may wish to transmit to the theatre.
This instruction leader will be of as- sistance to the exchange in that it will facilitate the special handling required in the exchange for the various types of prints, by providing an easily noted means of identification for each type.
Various Designations on Prints
It should be noted that the designation "Regular" in the Fader Setting Instruc- tion Leader indicates that only one type print has been issued on the particular production under consideration. Pro- ductions with prints designated as either "Hi-Range" or "Lo-Range" will have been issued in both type prints, i.e., all productions on "Hi-Range" prints will have necessarily been issued on "Lo- Range" prints as well
This instruction leader will also en- able the projectionist to identify a print which requires a "push-pull" reproduc- ing system as contrasted with a print requiring a "single" system.
Lab. Strikes Out 1 Term- In order to identify more plainly the "push-pull" or "single" system prints, it was decided to include both the terms "push-pull" and "single" on every leader, crossing out in the laboratory
FIGURE 6
Standard fader instruction leaders
one or the other of these two to leave the appropriate term designating the type sound track on the print. The illus- tration of the Instruction Leader in 5 and 6 indicates the manner by which this was accomplished for leaders which would be included in prints containing a sound track for reproduction on a "single" system. For leaders to be in- cluded in prints containing "push-pull" tracks the word "single" would have been crossed out, leaving the word "push-pull" to indicate this type of track.
In order that the projectionist may achieve the best results, the fader set- ting designated in this leader should be followed in general, inasmuch as the en- tire balance between the dialogue and music throughout the reel will be chosen for each designated setting.
News Notes
THE I. A. was much in the news of the past month. First, the five studio locals voted overwhelmingly in favor of I. A. General Office supervision for an indefinite period. I. A. and RCA finally agreed on a contract covering all RCA theatre servicemen in a deal similar to that closed recently between I. A. and Altec.
Society of Sound Engineers, un- affiliated N. Y. City group, wired Presi- dent Green of A. F. of L. and asked why I. A. had refused them a charter; why I. A. has signed contracts covering theatre sound service without consulting the engineers, and why I. A. seeks to destroy Society by allocating several servicemen to each I. A. local.
All-Canadian Labor Congress, opposed
to A. F. of L. units in Canada, charged that I. A. forced cancellation of all road stage attractions in a Canadian theatre because I. A. men were not employed therein. Excerpt from petition to Cana- dian government:
"Surely it is not too much to ask the government to find some means whereby it can protect the right of Canadian workers to establish and maintain their own independ- ent unions. Members of United States unions who are permitted to enter Canada to fulfill engagements here do so by the grace of the government, and if they use boycotts or sit- down strikes in the attempt to destroy Can- adian unions, it is not unreasonable to sug- gest that the government is bound to take cognizance of such activities."
Poor Canadian Prints
Canadian exhibitors, on the warpath over the poor condition of film prints, have named a Better Prints Committee.
January 1938
INTERNATIONAL PROJECTIONIST
27
Complaint covers scratches, sprocket holes and poor splices. Exhibs assert too few prints are in circulation, with subsequent runs getting the worst of it.
Canadian motion picture theatres have increased by 227 to a total of 1,089 in 1937, with majority of new houses being under 500 seats.
S.M.P.E. Washington Convention
The next convention of the S. M. P. E. will be held at the Wardman Park Hotel in Washington, D. C, April 25-28. The Fall meeting is scheduled for Detroit sometime in October.
17,000 Active U. S. Theatres
There are 17,000 active theatres in the U. S., according to film czar Will Hays. Approximately 740 new theatres were opened during 1937. Hays estimated
theatre attendance at 12 million daily, reflecting a weekly gain during 1937 of 1 million patrons. Picture business has a capital investment of 2 billion dollars.
N. Y. State 2-Men Bill
N. Y. State Federation of Labor will handle and push aggressively in N. Y. Legislature bill compelling all theatres in State to employ not less than two men on each shift. Labor is very strong in legislation right now, thus chances for passage of manpower measure are bright.
A. P. S. Installs New Officers
Annual meeting of American Projec- tion Society on Jan. 10 witnessed in- stallation of new officers by P. A. Mc- Guire, honorary member of Society. Executive roster now is W. Byrne, pres.; A. R. Bishop, v.p.; Frank McMahon, sec; T. Rugino, treas.; and J. Chul- cbian, sgt. at arms. Governors are J. Burgundy, A. Polin, B. Norton, T. D. Smith, H. Levene, and H. Grabelsky.
Barrows-Burke 20th Term
Thad Barrows and Jimmy Burke have been re-elected as president and business representative, respectively, marking twenty years service by these men in same posts. Other officers B. McGaffigan, v.p.; A. Moulton, fin. sec; J. Rosen, treas., and an executive board of L. Piro- vano, J. Nuzzolo, and J. Gibbons.
Altec-RCA Service Control
Recent acquisitions by RCA and Altec of so-called independent theatre servic- ing groups throughout the country indi- cates that these two I. A.-organized out- fits intend to stand alone in the theatre servicing field. I. A. can, and probably will, assist materially in this drive by barring from unionized theatres all non- union servicemen. Naturally, no ex- hibitor can be forced to take service that he doesn't want, but number of these is few, the result of the sharp drop in serv- ice rates during the past few years.
, „ .|! i
Loew's, 20th Century Profits
Two major film companies show healthy statements for their last fiscal years. Loew's, Inc., had net earnings of $14,426,062 after all charges, equal
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28
INTERNATIONAL PROJECTIONIST
January 1938
to $8.62 a share on outstanding common stock. Net earnings for 20th Century- Fox approximate $10,000,000, with cur- rent year expected to be better.
Hit Stars Radio P.A.'s
The appearance of film stars on radio programs throughout the week is a far more serious matter to the picture busi- ness than are horse and dog tracks and other events which compete with the theatre for patronage, according to Jack Cohn, vice-president of Columbia Pic- tures Corp. The Third (N.E.) District of the I. A. recently expressed its opposi- tion to pari-mutuel betting.
Cohn said that film stars on the air place the movie industry in the position of having to sell that which the radio gives away — entertainment. Exhibitors generally are burning over these air ap- pearances, but producers not only will go along with their exhibitor customers but actually compete with each other in sponsoring big radio shows.
Radio executives attitude is that pic-
The real low-down on amplifier circuits in the book SOUND PICTURE CIR- CUITS. 208 pages of informative text; illustrations printed separate from text; insuring constant ready reference. Last edition now almost gone. Order direct from I. P. for $1.75, postage prepaid.
ture industry should stop "fussing" about film players on the air and be grateful for all the publicity accorded pictures by air shows.
TELEVISION PROBLEMS: A
DESCRIPTION FOR LAYMEN
{Continued from page 23)
higher than used in previous radio serv- ices. This has required development of new tubes and circuits to generate, am- plify and control them. It has required the study of their behavior in space, so that we could know how far and with what results these new waves would travel.
The problem of synchronizing the re- ceiver with the transmitter has been diffi- cult. It has been solved, but to obtain the solution has required extraordinary amounts of research, patience, ingenuity, time and money.
The problem of network connection of stations, to permit syndication of a pro- gram, remains to be solved. Various problems of economic sort having to do with location and cost of stations, and programs, are dependent upon this tech- nical problem.
The problem of increasing the size of the reproduced picture in the receiver
still is with us. We expect to solve it, and we probably will. But if we do not, we may well be grateful and content that clear vision of distant events has been given to us, even if not quite as con- veniently sized as we migbt like.
There is one problem which is not an engineering one, strictly speaking, although there is close mutual depend- ence between it and technical develop- ments. This is the program or studio requirement. No matter how excellent the technical facilities may be, the whole system is a loss if those things put be- fore the "Iconoscope" are not interest- ing to the watchers at the "Kinescope." Whenever a new technical service is pro- vided, time is required to find out how to use it. Its strong points and its weak points have to be discovered by experience — the former capitalized and the latter avoided.
If television had come to a world which knew nothing of sound broadcast- ing or of motion pictures, any kind of program material, no matter how poor, would have been acceptable initially, and improvement in program to good stand- ards might have been allowed to take considerable time. But television will come to a world already accustomed to
IT IS WISE
To have reserve illuminating power for projection
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Not to provide a light source of suffi- cient volume to spread good light all over the picture with enough to spare for the more dense feature prints.
Consult
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Type HC-11 Projection Arc
24 Van Dam St.
New York, N. Y.
January 1938
INTERNATIONAL PROJECTIONIST
29
reproduction of sound and pictures hav- ing very high program excellence and effectiveness. If the television receiver is to have interest longer than a few days after its purchase, the program it delivers must supply the interest. There- fore it is necessary to solve the studio problems of television — the lighting, make-up, costuming, scenery, scenarios, actors, and all the rest — before television can be made a public service.
Place in Amusement Field
Questions are often asked concerning the possible effect of television upon sound broadcasting and sound motion pictures. The answer is simple, and the gift of prophecy is not needed in order to be able to make it. The an- swer is apparent from the outcome of many similar situations in the past. The telephone did not supplant the tele- graph; it supplemented it. We still have messages to transmit which do not re- quire person-to-person conversation. The telegraph cannot serve as telephone, but neither can the telephone do things which the telegraph can.
Similarly, sound broadcasting did not ruin the theatre and the motion picture. Instead it added to their appeal and their profits. At first there were many fears. Opera managers would not per- mit performances to be broadcast. Box- ing promoters would not permit their fights to be heard over the air. But after things settled down, the actual re- sults were — the million-dollar boxing gate, the S. R. 0. sign in opera houses, the addition of sound to the motion pic-
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Efficient ventilation, the pulse of the whole machine, is scientifically assured. 16 ad- justments for arc voltage control under all conditions are provided.
Installations of Brenkert R-6 Rectifiers are increasing by landslide percentages. For the theatre that must transform its cur- rent to d.c. for low-voltage projection lamps, R-6 will stabilize operations and reduce current bills.
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ture, and increased public interest in the theatre generally.
And so it will be with television, no matter how excellently that develops in years to come. There will be some things which television can do which previous arts could not do, a few things which it can do better, but there will be many things which they can con- tinue to do which television cannot do at all. So they will continue, and we shall have added another art and public service to the continually growing list. As a matter of fact, rather than being harmed by television, many of the older services are going to be helped, just as the silent motion picture was enabled by radio sound apparatus to find its voice and expand its possibilities. The older arts will find much help from the gadgets of television, should therefore welcome it, and need not fear it.
The Pressing Question: When?
Only one problem remains to mention. It is one which is encountered by tele- vision workers more frequently than any other. It is the question "When will we have television?" That is one prob- lem which has not been solved! A simple answer is not possible, because
the question is not simple without sev- eral definitions. We have television right now, under the definition of tech- nical possibility. We will probably have it in a year or two if we limit the defini- tion to include only those people who live within a few miles of a station, with only two or three stations in the coun- try.
However, if we mean when will tele- vision service be available to most of the people of the country, it seems safe to say that the years between then and now will be goodly in number.
ANALYSES OF NEW THEATRE REPRODUCING EQUIPMENT
(Continued from page 19)
grid and the plate. The suppressor grid is tied to the cathode, either internally or at the socket, and therefore is posi- tive compared with an electron, although commonly thought of as negative because it is negative compared with the screen grid and plate. Its presence discour- ages secondary emission from the plate, where the screen, unshielded by a sup- pressor, had the opposite effect. The five-element tube, or pentode, built in this way, is capable of enormous ampli-
30
INTERNATIONAL PROJECTIONIST
January 1938
fication as compared with the simple triode.
These considerations may lead some to think that introduction of gas, which also increases the value of the space current, might promote amplification, but such is not the case. The action of the gas depends upon the motion of the gas ions — atoms that have lost one or more electrons. Ions are extremely heavy compared with electrons, 1800 times as heavy at the very least. Their weight or mass prevents them from reacting easily to the slight, quick changes of grid voltage that represent audio fre- quencies.
Increased plate current due to the presence of gas is not accompanied by
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increased amplification, and elaborate and rigid processing is used in the manu- facture of amplifying tubes to keep gas out of them. Among other things, the metal parts are heated to incandescence, and the glass almost to the point of fusing, to drive occluded gasses out of those materials before the pumping stops and the vacuum is sealed.
The type of amplification described, in which the grid carries a permanent nega- tive bias which is varied to a slight degree by the input pulsations, is Class A amplification.
In Class B circuits the permanent grid bias is either zero or very low. Thus, when the incoming pulsation is negative the grid bias is increased; but at the positive input swing the signal voltage is stronger than the permanent bias (if any) and the grid goes positive. The result is an immense temporary increase in space current, as the grid attracts ^mission instead of repelling it. Some of the electrons are captured by the grid, resulting in a flow of actual grid current, but the majority go on to the plate, constituting a sudden surge that represents enormous amplification.
In these circuits, the fact that the grid attracts electrons at some parts of the cycle, and carries real current, means that it cannot be coupled to the signal source through a high resistance. Also, the signal source cannot be a voltage amplifier ; the grid must be supplied with current as well as with voltage, hence with power. The signal source for a Class B amplifier or stage of amplifica- tion is called a driver amplifier or stage, and in a theatre system may have an output of several watts.
Class B amplification is seldom very free from distortion, and a compromise
arrangement is known as Class AB. The grid carries a permanent negative bias of moderate value. As long as the vol- ume remains low, the amplifier works essentially as a Class A circuit, in which the input signal is up or down, but never to the point where the grid becomes posi- tive. However, when the signal volume increases, the input may overcome the grid bias completely, swinging the grid positive and resulting in Class B opera- tion.
This arrangement has a number of advantages. The relative freedom from
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January 1938
INTERNATIONAL PROJECTIONIST
31
distortion characteristics of Class A is obtained at all lower volume levels, which is where distortion is most notice- able. When sound is very loud, distor- tion is more difficult to distinguish. At the same time a smaller, cheaper ampli- fier is made capable of putting out vol- ume that would require larger tubes and parts if the operation were maintained at Class A under all circumstances.
In a Class A circuit the grid is biased at a point at which no signal will ever
be strong enough to overcome the permanent voltage and drive the grid positive. However, unexpectedly strong signals may upset this anticipation, caus- ing a Class A grid to draw current and work temporarily as Class B. When this happens the plate current meter fluctu- ates visibly, and the amplifier is said to be overloaded. It is also in some danger of burning out, since its parts are not designed to carry the resultant surges of plate current.
S.M.P.E. Discussion of Stereoscopic Pictures
(Continued from page 13)
defects of registration and eye-strain go hand-in-hand.
Mr. Wheelwright: Some eyes are better st ereoscopically and stronger than others. I am trained to use my eyes to such an ex- tent that I am a very poor guinea pig to try the pictures on. People with sensitive eyes, or who use one eye to the exclusion of the other, are very much more conscious of eye-strain than I. I can assure you that pictures can be properly taken and can be properly shown so there is no eye-strain.
Mr. Freedman: When I tilted my head to one side, the registration became accurate.
Mr. Wheelwright: That is correct. The reason was that the planes of polarization are fixed as regards the projector, but you change the planes of polarization of the glasses when you tilt your head. The effect can be overcome by another method of polarization into which I do not now care to go.
Mr. Griffin: Mr. Wheelwright's paper sketched the history of stereoscopic systems. We might include therein mention of the "Teleview" system, which did not require audience to wear glasses. The system was installed in the Selwyn Theatre, New York, about 17 years ago. It projected two-eye pictures from two projectors running syn- chronously, the unit driving the projector motors being connected through a distributor driving small synchronous shutters con- nected to the seats for each viewer. The shutter cut-off alternately the left- and right- eye pictures so that the results were identi- cal with those we are getting here.
Mr. Kellogg: How good is the screen in preserving the polarization? Can you scat- ter the light as much as needed without loss of polarization? What is the tolerance,
or how much must the image for the wrong eye be reduced for practical purposes? How does the effect depend upon the general illumination level? It seemed to me as if some of the figures were distinctly out in front of the screen.
Mr. Wheelwright: If the screen has a metallic surface, or certain other surfaces that are satisfactory, there will be no loss of polar- ization. Certain other surfaces are com- pletely unsatisfactory. For example, a plain white surface is very bad; an aluminum screen is practically perfect. There are all sorts of variations between.
Mr. Kellogg: To what extent must you suppress the unwanted image?
Mr. Wheelwright: Fairly completely, depending upon the lights and darks in adjacent areas. In other words, if a pic- ture is of the same order of brightness throughout, then polarization will have to be very complete. In these pictures it is fairly complete, provided you hold your head substantially parallel to the projector, which most persons do by choice to get the best registration. That is the secondary problem, since we know a way of getting around it completely if it seems to be a serious problem.
Mr. Kellogc: Presumably the higher the level of illumination, the more exacting the requirements for suppression.
Mr. Wheelwright: That is right, and the greater the differences. The out-in-front effect is controllable at will. In some of these pictures it is being shown to a greater degree than I should have chosen. We know the laws now well enough to control it, and in making a commercial or semi-com- mercial film we can completely control
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PROJECTIONIST
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No other test equipment offered to the projectionist will measure accurately the voltage on the photo-cell, or the plate and grid voltages in resistance-coupled head amplifiers.
Breakdowns are reflected in the box-office. The 4800 S will help prevent breakdowns and help locate the trouble quickly when the sound stops or "goes sour".
Hickok — designed by engineers who have had actual experience in, and are in constant contact with problems of, the projection room, the 4800 S has many features which make it the finest tester for projectionist use. A.C. and D.C. volts, A.C. and D.C. milliamperes, amperes (using ex- ternal shunts which require the absolute minimum of extra wir- ing); resistance, capacity, deci- bels, inductance, tube test by grid-shift method, and the zero- current voltmeter for voltage measurements in high-resistance circuits.
Exactly as described by Brother Robert Garwin in June, 1937, issue of International Projectionist
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32
INTERNATIONAL PROJECTIONIST
January 1938
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whether it occurs in front or in the back- ground, or to -what degree.
Mr. Kellogg: Does the out-in-front effect depend upon the distance of the observer from the screen?
Mr. Wheelwright: To a minor degree. If you sit very far back from the screen the depths are exaggerated. If you are very, very close, there is a sense of intimacy, but not so much depth as would be seen from way back. From the side, as long as each eye sees substantially the same brilliancy as the other, you will get a better sense of reality in the pictures than in a normal flat picture, wherein everything becomes dis- torted when viewed from a point at the side. We can control that with the metallizing of the screen, something we have been study- ing on the side. There has to be some metal in the base of the screen.
Mr. Mole: Have enough persons viewed these pictures to provide statistical informa- tion on possible anomalies in vision? I noticed, for example, what may be an in- dividual idiosyncrasy, though nobody com- mented upon it — a secondary image off to the side of the screen.
Mr. Wheelwright: That is what might be called a vignetting problem. Since these pictures were taken and this projector built, the effect has been completely eliminated.
Mr. Schultz: I noticed when looking through these glasses that a great deal of light seemed to be lost. Have you informa- tion on the proportion lost, or is it that the glasses are imperfect?
Mr. Wheelwright: That is not because ihe glasses are imperfect; that is the penalty we pay for polarization.
Mr. Schultz: Would the average theatre be required to increase its screen illumina- tion?
Mr. Wheelwright: Something would have to be done about the problem.
Mr. Friedl: You stated that the surface of the screen must be metallic. Ordinarily, I regard reflections of non-polarized light from metallic surfaces to be partially polar- ized. If in projection you use polarized light, will not the reflection from the screen depolarize it?
Mr. Wheelwright: Polarized light can be scattered to a great degree and remain polarized, or it can be reflected from a sur- face and still retain some degree of polariza- tion. There is a difference in reflection from metallic and non-metallic surfaces. To retain polarization to a great degree the surface must be metallic or partly so. Fabric surfaces destroy the effect, depend- ing upon the pigment and texture of sur- face. It is quite complicated.
Mr. Lewis: Can stereoscopic pictures be shown in the usual projector?
Mr. Wheelwright: Yes, with a supple- mentary lens or device in front of the lens.
Mr. Lewis: Is it not necessary to reduce the picture width, as shown here?
Mr. Wheelwright: As I mentioned, this equipment is experimental. There is no reason why the frame shape should not be the same. There will, bowever, be less film area per eyeview than there would be with ordinary pictures; but if you take the two eye pictures and add them up, there will be the same amount of information for the two eyes as before, but subdivided in a new way.
Mr. Lewis: If you used the standard 35' mm. projector and projected the pictures in the same size of room, would you have to reduce the area of the picture?
Mr. Wheelwright: In very large-sized projection you certainly would have to re- duce the picture or increase the light. In the smaller pictures we think we can get away with it.
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% But every one of them has to prove it before it's okayed for your booth — and more than once, too. First, it has to back up the claim on the inter- mittent movement test line. Here "the heart of the projector" is run for 12 hours. It's checked for the slightest irregularity of operation — checked for any trace of grease leak.
Again, after the complete mechanism has been assembled it has to prove itself in a two day work-out — 48 hours of continuous operation. Again it has to "take it" — and without making any noise about it either.
Finally, in 6 hours of actual operation under the heat of a high intensity lamp — it handles film that is patched every 15 or 20 feet. And the picture must be rock steady.
When a mechanism has proved it "can take it" in these tests it has earned its right to the name Motiograph — In Pro- jection—"The Standard Of The World." But there's more to the story than just tests. Why not stop in at your Motiograph distributor's display room? Let him show youMotiograph's convenience features,the precision craftsmanship, and the quality materials that have gone into its building.
# Incidentally, in talking to the boss about those new projectors you need, don't forget to remind him of Motiograph' s Deferred Payment Plan. It enables him to collect the dividends on good projection, immediately, and with only a small cash outlay.
THE PROJECTOR PRICE COMPLETE, $1f)7C LESS LAMP AND SOUND REPRODUCER ILiJj
F. O. B. Chicago
Motiograph, inc., Chicago, u.s.a,
INTERNATIONAL PROJECTIONIST
February 1938
HEED THE HANDWRITING
ON THE SCREEN
W
% Now that one theatre in every three has high in- tensity projection, every theatre owner without it faces a new situation. Theatres using high intensity have 75 per cent of the country's total seating capacity. They also are the theatres best attended and paying the most profitable return.
Obviouslv, if thousands of theatres have installed
Get the facts. I^J?£^£ of every advantage that h ^
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high intensity projection, high intensity projection cannot be expensive. Its really low cost will surprise you. Peerless Magnarc Lamps produce 200 to 300 per cent more light on the screen for the same current cost as low intensity.
You need high intensity projection not only to hold, but to increase your patronage.
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February 1938
INTERNATIONAL PROJECTIONIST
R0JECTI0N1S1
With Which is Combined PROJECTION ENGINEERING Edited by James J. Finn
Volume 13
FEBRUARY 1938
Number 2
|
5 |
Outdoor Theatres Utilize New |
||
|
Craft Tricks and Troubles of the B. S. Projection Era . . . |
7 |
Projection Set-Up, Technic. . George L. McGovern |
22 |
|
A. C. SCHROEDER |
As One Old-Timer to Another. . |
23 |
|
|
New Standards For Old Thad C. Barrows |
11 |
E. Klingensmith, S. Robbin and A. C. Schroeder |
|
|
Notes on Capacity and Conden- |
12 |
Analyses of Modern Theatre Sound Reproducing Units, III |
24 |
|
L. P. Work |
Aaron Nadell |
||
|
New Simplex E-7 Projector Has |
17 |
Contest Winners and Awards . . |
26 |
|
The New Simplex E-7 Projec- tor: A Graphic Story of Its |
19 |
Notes From the Supply Field . . News Notes |
28 |
|
The Place of Television Among |
20 |
Technical Hints |
|
|
Dr. A. N. Goldsmith |
Miscellaneous Items |
Published Monthly by
JAMES J. FINN PUBLISHING CORPORATION
580 FIFTH AVENUE, NEW YORK, N. Y. Circulation Manager, Ruth Entracht
Subscription Representatives
Australia: McGills, 183 Elizabeth St., Melbourne New Zealand: Te Aro Book Depot, Ltd., 64 Courtenay Place Wellington England and Dominions: Wm. Dawson & Sons, Ltd., Pilgrim St., London, E. C. 4.
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States and possessions, $2 (two years, $3) ; Canada and foreign countries, $2.50. Single copies, 25 cents. Changes of address should be submitted two weeks in advance of publication date to insure receipt of current issue. Entered as second-class matter
February 8, 1932, at the Post Office at New York, N. Y. under the act of March 3, 1879. Contents copyrighted 1938 by James J. Finn Publishing Corp. International Projectionist is not responsible for personal opinions appearing in signed articles in its columns.
MONTHLY CHAT
THIS month we take leave of the so- called big fellows stationed in the iarger theatres (these worthies being well able to take care of themselves) to point without pride to and view with considerable alarm a situation which is the peculiar concern of those projection- ists (and owners and managers) who man the medium- and small-size theatres of this country — -nay, of the world. Credit a lamp manufacturer for starting us out on this tack.
We received our first shock when in- formed that a. c. arc lamps still are being shipped, and in no minute quan- tities, to theatres everywhere. This news was somewhat of a blow to our pride, because we thought that this trinket had been decently interred for lo, these many moons. But no; and who are we to question on-the-level shipping records? Well, there might be some excuse for the purchase of a. c. lamps after all, even if only on the score of economy through ducking the purchase of con- verting equipment.
BUT the shock to end all shocks was yet to come. Our informant next proceeded to cite the shipping records on low-intensity lamps, orders for which were placed even after the strongest pressure in favor of Suprex had been exerted. This finished us, even if the next announcement were to be that 700 Edi- son Kinetoscopes had been installed in the U. S. within the last three weeks.
Now, we are not unaware of the fact that certain projection men profess to a strong dislike for the Suprex arc, al- though we have never been able to pry loose from these fellers their reasons therefor. We're quite willing to let it pass on the basis that these reasons are private and personal. But when the answer turns out to be preferment of the low-intensity arc over the Suprex, then it is high time, as they say in letters to editors, that something was done about it. So say we, too.
Irrespective of what yardstick is em- ployed— whether it be quantity or qual- ity of screen illumination, or lumens per dollar of cost, or suitability for color film — Suprex leads low-intensity by sev- eral hundred miles. Lives there a pro- jectionist so dense as to be unable to recognize Suprex superiority over the 1. i. arc? Supply dealers, we hold, have done a not-too-good job with Suprex; but we should be mortified to find one of our fellows voting for the 1. i. arc.
SOAK up the data on that new Sim- plex E-7 which is described in word end picture within this issue. We couldn't hope to cover all angles of this unit in one fell swoop, so if there are any questions popping, let's have 'em. A new model projector is one of those rare events, its introductory period the one time we can snitch all the dope we want.
SHOW
^^^ ^^ Simplified High Intensity Projection makes the
^ good show possible. Get the powerful, modern,
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BRENKERT ENARC
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Brenkert Enarc operates at top efficiency with every projector, because it was definitely engineered to do so.
Consider this example: on the Monograph Projector illustrated, the standard Brenkert Enarc Lamp is the only lamp providing all the following important features:
I* The light is completely enclosed, from lamp to film.
2* Full 12-inch positive carbon trim at one setting is provided, with space to spare between end of carbon and light dowser.
3* Correct distance from lamp reflector to film, for clear screen illumination and greatest efficiency, has been assured.
Users of Brenkert Lamps enjoy this cor- rect engineering, plus superb service, at no extra cost
So specify BRENKERT ENARC— always! and realize complete satisfaction.
BRENKERT LIGHT PROJECTION CO
ENGINEERS AND MANUFACTURERS
DETROIT, MICHIGAN, U. S. A.
INTERNATIONAL PROJECTIONIST
VOLUME XIII
NUMBER 2
FEBRUARY 1938
Craft
Tricks and Troubles of the B. S.* Projection Era
By A. C. SCHROEDER
MEMBER, PROJECTIONIST UNION 150, LOS ANGELES, CALIFORNIA
SOME of us like to gab about our early projection experiences, days when our projection knowledge was quite limited. Younger projectionists either listen in wonderment and with envy to the stories of the past, or they scoff, saying it is just "hooey."
Old-timers -remember the small lamps wt had and how the carbons grounded against the top or the floor of the hous- ing. The arc was right off the line through a rheostat (unless the supply was a.c. when the rheostat might be replaced by a transformer). Everything in Los Angeles was Edison three-wire, thus on one side of the line the lower carbon grounded; on the other side the upper carbon grounded. The lamp- house roof was sometimes lined with mica to prevent the upper carbon grounding. Probably this is why the Powers 6-A had a much taller lamp- house and also the extended part on the lower front wall, giving more room so
*Before sound. (As though you didn't know.)
We haven't inquired of the author as to the reason for this flight of remin- iscence, but we suspect that it was in- duced by the barrage of brickbats thrown in his direction by those who were nettled by his reference last month to "button-pushers" and his commendation of the up-and-coming younger craftsmen. (See article "As One Old-Timer to Another" on page 23.) Anyhow, the oldsters will read this with keen appreciation; while the youngsters — well, they just won't be able to imag- ine such goings-on. — Editor.
the lower carbon could not contact it. We used to fuss with the adjustment (so-called) for aligning the carbons on the Powers 6. Adjustments were not brought out of the lamphouse, but were right at the burner, and were adjusted when trimming the lamp. Loosening a brass knob, which clamped the adjust- ment, we moved the knob back or forth, swinging the top carbon into alignment
[7]
with the lower carbon. The knob was then tightened, holding the carbons in line. Oh, yeah? It would, if the lamp were perfect, but most of them were soon junk, and the carbons quickly be- came misaligned. We then opened the lamphouse, and with pliers in one hand (remember the other hand was turning the crank ! ) we again aligned the car- bons.
The adjusting screw was hot, elec- trically, and hotter than blazes other- wise. The light was blinding, so we could not see what was going on. We could only guess, then wait till the crater formed again to see if the spot was round. Those were the good old days.
Tricky Carbon Adjustments
We "saved" carbons even that far back, and sometimes ran short. At other times we had sufficient carbon in the lamp, but most of it was above the up- per jaw, or below the lower jaw; we for- got to shift the carbons. With one hand
INTERNATIONAL PROJECTIONIST
February 1938
still on the crank, the arc was lengthened as much as possible (which was quite a bit on a 110-volt line) ; the upper carbon clamp screw was loosened until the car-
The smaller \ \ offers less \ \ obstruction to \ \
the light -]7i\ \
FIGURE 1
bon dropped of its own weight, then the screw was tightened and the arc ad- justed to the proper length. When the carbon dropped it went down until it hit the lower one, and the light on the screen was practically nil for a few seconds.
Raising the lower carbon was more tricky. The clamp screw was loosened slightly, so the carbon could slide when twisted with pliers and pulled upward. The entire lamp being loose and wobbly, the spot at the aperture wandered around and the picture was poorly illuminated during the operation. After this procedure one's left hand was often blistered from the heat.
Edison and Bio were the only car- bons, at least on the Pacific Coast, and the size was usually % inch. The same carbons were used above and below (positive and negative to you). Eventu- ally the silver-tip carbon appeared. With one of these carbons in the lower jaw, wc had an arc that did not sputter. Younger projectionists cannot realize what this meant. With the old carbons the arc would sputter if it was burned too short or too long, or if the alignment shifted slightly, which it often did.
Many attempts were made to improve conditions and obtain more light. In- stead of a %-inch carbon, considered standard, a ^-inch carbon sometimes was used below. This steadied the arc
FIGURE 2
and often produced more light, due to less obstruction by the smaller carbon, as shown in Fig. 1. A solid carbon was also tried below, that is, a carbon with-
out a core. However, the silver-tip stop- ped all that. Incidentally, the silver- tip was the forerunner of the coated car- bon of today.
Figure 2 shows other attempts to im- prove the arc and the light, showing dif- ferent relations of the carbons to each other. Each set-up had its adherents, who vigorously backed their method against any other. Fig. 3 shows further variations, the arc as a whole being tilted at different angles, with conse- quent advantages and disadvantages.
Versatile Projection Veterans
During the days when we cranked projectors we became very proficient with the free hand. Some projectionists wonder how a film can be spliced with one hand. The ends are carefully aligned on the bench, weights being used to keep them in position. It is surprising how rapidly and easily this is done with one hand, after a few years of practice. Fig. 4 shows the film with a weight on each end. The emulsion
within twenty seconds was pretty good, for a while. Soon the time required de- creased to ten seconds, for a complete thread-up. I say "complete" because
FIGURE 4
had been removed previously, also while the film was under a weight.
Fig. 5 shows one end raised by the scissors, so that cement can be applied to the other part. The scissors is then removed, allowing this end to fall inio position over the other piece. The parts will still be aligned because they have not been shifted, and pressure is applied with the fingers or another flat object is placed on the splice. This takes much longer than the modern method, but the projectionist had nothing else to do: he stuck around pretty close, turning the crank.
A one-armed man had nothing much oa us. Near the end of the show we got into street clothes and were ready to go when the show was over. (No time to get dressed after the break.) Managing a tie and a double-bow knot in the shoe laces with one hand was a daily occurrence. This was more com- plicated than splicing film, as we could not use weights.
Then there was the knack of making a fast thread-up, the time for which de- creased with practice. Turning the trick
FIGURE 3
this was reduced to seven seconds on an old Edison machine by a little "cheat- ing": the tail- pieces on all reels were cut off at the end of the picture. As the end came off the upper reel, it (the reel) was taken from the spindle and thrown on the bench. Remember that this happened while the machine was running and before the end of the film had passed the aperture.
The projectionist watched the end as it left the upper sprocket, and when it reached the aperture the light was cut and the machine stopped. The other hand was placing the next reel on the upper spindle, the right length of film for threading having been unwound previously and left dangling from the bench. (The rewind bench was always just to the right of the projector). The film was then placed on the upper feed sprocket, on the intermittent sprocket, and the gate was closed and the machine started.
This was all the time needed for threading. After the picture was on the screen the projectionist removed the full take-up reel, replaced it with an empty reel, threaded the lower sprocket and placed the film on the lower reel. The fact that the machine was motor driven at this time made things easier. Pro- jection speed was only 60 feet per min- ute, and during the latter part of the threading the speed was reduced even
FIGURE 5
below that. Such procedure obviously would be impossible today.
The writer improved the ordinary (Continued on page 34)
February 1938 INTERNATIONAL PROJECTIONIST
"TEN BEST" ON EASTMAN FILM EXCLUSIVELY
EVERY one of the "Ten Best Pictures" selected in the 1937 critics' poll of the Film Daily was "shot" on Eastman Super X Panchromatic Negative .... Release prints for" all ten were made on Eastman Positive .... An impressive double dem- onstration of Eastman's current contribu- tions to motion picture quality. Eastman Kodak Company, Rochester, N. Y. (J. E. Brulatour, Inc., Distributors, Fort Lee, Chicago, Hollywood.)
EASTMAN Positive and Super AT Negative
10
INTERNATIONAL PROJECTION IS
February 1938
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February 1938
INTERNATIONAL PROJECTIONIST
11
New Standards For Old
By THAD C. BARROWS
PRESIDENT, PROJECTIONIST LOCAL 182, BOSTON, MASS.
THE motion picture industry, too, is evidently suffering from the ailment of over-production. Having failed by a narrow margin to anesthetize the cash customers with three-hour programs which include two features, a newsreel and a short, the industry intensifies its drive toward the goal of self-extinction by setting up numerous new technical standards so that we may the more quickly forget the old, and by persisting in tolerating needless severe handicaps to the reproduction process.
I was much interested recently in read- ing a booklet published by the Academy of M. P. Arts & Sciences in which ap- peared detailed information relative to nine types of sound tracks together with data relative to projecting "Hi-Range" prints and to standard fader setting in- structions— all for the avowed purpose of achieving "maximum showmanship". What showmanship?
Some Current Shortcomings
Mention of the Academy implies no desire to attach all the blame for the shortcomings mentioned hereinafter to Hollywood; the exhibition field is equally guilty. The aforementioned book- let is tangible evidence that we have come a long way since 1930. But it might be a good idea if, before passing on to "Hi-Range" prints and other select technical company, we actually observed those standards established eight years ago. Consider first the Standard Release Print, the fruit of the first real coopera- tive action between production, distribu- tion and exhibition in the history of the industry, with which event we all are familiar.
Start marks are either misplaced or forgotten entirely. Changeover dots are placed on dark scenes, on moving objects and at times are missing. Twentieth Century-Fox apparently is conducting a guessing contest with projectionists by means of switching dots from the top to the center to the lower corner of the film frame. They still manage somehow to keep them on the right-hand side of the frame. The positioning of change- over dots on a dark background is tanta- mount to their elimination. And then the distributors moan and threaten to bill theatres for mutilated film when ha- rassed projectionists, particularly on one-man jobs, utilize their own markings or punches in order to put a show on the screen.
Mention of film density standards is futile: there are none. Even a 125-am-
pere. high-intensity arc light can't pene- trate some prints supplied to theatres. The manager or owner, mindful of his investment in high-intensity arc equip- ment and of his carbon and power bills, demands more light; and the projection- ist, unable to deliver beyond the limits of: his equipment, is blamed for all the errors made in the print on its journey from camera to the projector.
Another serious defect is the so-called "artistic" print, the product of certain "moody" directors (should we sav mouldy?) or of some old chromo who fights to keep the truth about her age from the cash customers by insisting upon what is termed a soft focus. We can get almost the same result with an inferior or oily lens, but the manager who pays top prices for good optics that produce a clear, sharp picture has yet to discover this.
Sound level standards are non-existent. Some current prints vary eight points on the fader. The present crop of studio musical directors apparently regard the print as a medium exclusively for the display of their own stuff; no intelligent soundman, unless coerced, would turn out recordings wherein incidental music is as loud as, or actually smothers, the dialogue. Result: theatre managers call for a few points lift on the fader, think- ing thus to favor the dialogue over the music.
Over-run sound tracks are quite com- mon. On many recent occasions I have seen sound tracks with a white line cut- ting into picture and making it impos- sible to fill the screen to the side mask- ing. Paramount News is very careless in this respect.
Warner Wants Wax
Waxed prints, an old evil once elimin- ated but resurrected by Warner Brothers despite the almost unanimous disappro- val of competent technicians, is again plaguing projection. Some Warner prints are so heavily waxed that it is almost impossible to keep the gate free from accumulated wax, the result of aperture heat. This is a common cause of severe distortion and not infrequently occasions a sound outage, in addition to causing an unsteady picture and possible scratch- ing.
The handling of film by exchanges leaves much to be desired. So badly dented are some cases that it is almost impossible to remove the film without serious damage. Reels are badly bent,
and at times the hubs are separated from the sides, the result of being dropped or rolled downstairs in an ex- change. Film handlers seem to regard the new large, heavy cases as indestruc- tible, which they most certainly are not. Some of this damage could be avoided by limiting the contents of the cases to three double reels.
It seems to me that before sounding huzzahs for the great technical advances being scored by the industry, as repre- sented by the wave of new "standards," we might with profit to all concerned pause to look backward down the road we have come. This statement implies no criticism of improved technique or of any proposed standard. But it must be obvious to all that unless those rules of the game, so to speak, applying to the fundamentals of the art, both in record- ing and in reproduction, are observed, the resultant errors will go far to cancel out, if not nullify, any subsequent im- provement.
Now — or in the Future?
The shortcomings mentioned in the foregoing brief summary, which by no means covers the entire range of defici- encies, have been the topics of numerous discussions among technicians for many years past; but there the matter rests. The solution of these problems requires no expenditure of money but merely the cooperation of studio, distributor and projectionist and a firm determination to eliminate these individually small but cumulatively big bars to better motion picture reproduction.
Meanwhile all this activity anent new standards reminds me of the harried businessman, who, having just signed a piomissory note, puts away his pen say- ing, "Thank God that's paid." Continued indifference to requests by projectionists for help in improving standards may one day cause the craft to lose interest in good reproduction on the theory that they don't make motion pictures but only show them, and are paid on that basis. When and if that day arrives, it may be toe late for Mr. Producer to regenerate such an unselfish interest in the presenta- tion of his product.
L. 244 HONORS P. A. McGUIRE
P. A. McGuire, for more than 20 years advertising manager for International Projector Corp., was elected an honorary member of Local 244, Newark, N. J., and also of the Local's social appendage, the Loyalty Club, at a dinner sponsored by the latter on Feb. 11. Mr. McGuire's ac- ceptance speech reiterated his deep in- terest in and support of the projection craft, which fact is attested to by his many-sided activities within and without the projection field in behalf of the art and the craft.
12
INTERNATIONAL PROJECTIONIST
Types of condensers for various applications
Notes on Capacity
and Condensers
By L. P. WORK
MEMBER, PROJECTIONIST LOCAL UNION 601
ELECTROSTATICS and the electric condenser play an important part in maintaining sound reproducing equipment at the level of best perform- ance. After the early faults in the equip- ment are found and corrected, a large part of the usual run of trouble is asso- ciated with three types of parts, namely, tubes, resistors and condensers. Tubes may easily be changed and a quick check by substitution had without any special test equipment; resistors are easily checked for continuity and ohmic value with simple meters; but con- densers are prone to hiding their faults — in fact, sometimes a condenser fault cannot be disclosed by instruments at all.
In the past twenty years this subject has been somewhat neglected in the regular college engineering course, but in recent years with the wide expansion in the electronic arts more attention is being given. Before continuing with the applied phases of the subject, let us consider the electrostatic theory of the device.
Man's earliest knowledge of electricity was that of frictional charges on amber and other "electric" substances which, the ancients discovered, would attract or repel other light bodies on being rub- bed. An experiment in physics com- monly used to illustrate electrostatic flux lines about a charged body is shown in Fig. 1, wherein a highly-charged rod A pierces the horizontal glass plane B upon which finely divided cotton lint is sprinkled. The lint will be quickly ar- ranged along the radial lines of the arrows, this action taking place without
flow of current in the rod — merely the presence of potential. This charge on the amber is the same as the static potential resting in the dielectric of a condenser.
The condenser is unique among all electric devices with which we deal in that it is the only one which functions as a static storage medium. A theoretic- ally perfect condenser will store a charge indefinitely and at any future time dis- charge the same quantity as it received. An elementary perfect condenser is shown in Fig. 2A wherein the plates PI and P2 are separated by the perfect dielectric D. When a voltage is applied to PI and P2, a flow of current takes place momentarily until the condenser is "full" and equilibrium is reached. This inward flow of current is stored electrostatically, the quantity being pro- portional to (a) the area of the plates, (b) inversely proportional to the dis- tance between the plates, and (c) di-
FIGURE 2
PI
February 1938
The quantity of electricity stored by a condenser is measured in coulombs Q, which is the number of electrons per second a potential of one volt will force through one ohm of resistance. The capacity of a condenser is defined as one farad, if when one volt is applied, a charge of one coulomb is stored. The farad in relation to the henry and the ohm is too large for general use, so the microfarad (mf, one-millionth part), or the micro-microfarad (mmf, one million- millionth part) are adopted as working units.
If the capacity of this condenser were measured with dielectric D removed, and later measured with it, it would be found in the second instance that the capacity would be increased several-fold even though the area and spacing of the plates were unchanged. This is due to the greater permittivity (designated K) of the dielectric compared with air, which is the standard. With air hav- ing a permittivity of 1, some common dielectrics run as follows: glass, 5-8; paper, 1.5-2.5; oils, 2-2.5, and mica, 2-6.
A high permittivity is only one of sev-
eral properties a desirable dielectric should have: it should be of high re- sistivity to prevent leakage of the charge from one plate to the other; it should be of good dielectric strength to with- stand puncturing strains; it should have low intermolecular friction when under alternating electrostatic stress to min- imize heating. These desirable qualities do not necessarily go hand in hand in a given material: for instance, electric
Rl
R2
] d f^^^p v;;;;;/////;;,7*
P2
rectly proportional to the relative per- mittivity or specific inductive capacity of the dielectric.
B
slate and glycerin have K factors of 30 and 56, respectively, but their leakage would be too high to be usable. The
February 1938
INTERNATIONAL PROJECTIONIST
13
7-A
ce
Reg. U. S. Patent Office
Motion Picture Projector Complete
consisting of the Wenzel "Ace" projector mechanism with built-in rear shutters, 18-inch magazines, "Ace" soundhead (WSH model), and De-luxe Universal Pedestal.
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Adaptable to all other soundheads and lamphouses.
Contact your dealer regarding the Wenzel "Ace" pro- jector mechanism with rear- or front-shutters, light- weight 5-point Type L pedestal, "Ace" double-bearing intermittent movements, rear shutters, rewinders (hand and automatic), replacement parts for "Ace", Simplex, Kaplan, Powers and Motiograph projectors. Special sprockets, film cabinets, magazines and amplifiers.
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NOTE: Above distributorships do not apply to Ashcraft lamphouses.
14
INTERNATIONAL PROJECTIONIST
February 1938
PLENTY OF PROBLEMS-YES
. . . but the big problem, how to increase public interest in motion pictures, is easy to solve. Here's the answer. Simplified High Intensity projection that puts picture quality on the screen, makes every picture seem a better picture, whether it is black and white or color.
When you install Simplified High Intensity projection you put your theater in line for successful competition with the best houses. You are giving patrons as much for their money as they get anywhere.
Yet this modern projection is not expensive. It gives two to three times as much light on the screen, but at so much less cost per light unit, that one admission per show will cover it.
More than 3500 theaters have installed Simplified High Intensity projection during the past four years. Theaters accounting for a majority of the nation's seating capacity now offer modern high intensity pro- jection. So should you.
Write for new, illustrated free booklet, "The Eternal Triangle in Picture Projection.
SIMPLIFIED
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Copyright 19:j«, National Carbon Company. Inc
NATIONAL CARBON COMPANY, INC.
Unit of Union Carbide HIM and Carbon Corporation
CARBON SALES DIVISION, CLEVELAND, OHIO
General Offices: 30 East 42nd Street, New York, N. Y. BRANCH SALES OFFICES: _ NEW TORN PITTSBURGH CHICAGO SIB FRANCISCO.
February 1938
INTERNATIONAL PROJECTIONIST
15
dielectrics used commercially are those which can best be handled and still afford usable capacities at reasonable costs, such as paper and mica; the elec- trolytic condenser which uses a chemical film dielectric we will consider sepa- rately.
The need of high ohmic resistance can easily be seen in the case of blocking condensers used to couple the plate of an amplifier tube to the grid of the next stage. This condenser passes the a.c. component of the signal, but must not have enough leakage to allow the posi- tive plate potential to alter the much smaller negative potential on the grid of the following tube, otherwise the suc- ceeding stage will distort. And a very small leakage will do this because of the normally high resistance to ground of the grid circuit which makes the IR drop considerable even with minute cur- rents. A situation similar to this obtains in the majority of applications in sound equipment, i.e., a.c. must be by-passed with very small d.c. leakage.
Dielectric Strength
In any insulator the thickness of which is definitely limited as in a condenser, the problem of strength against direct puncture basically influences choice be- cause it is this puncturing strength which sets maximum, hence working, voltage. If we increase thickness, we decrease capacity because of the greater plate separation and thus lose the advantage of a good K factor ; also, a slight increase in thickness means a great increase in the size of the finished article.
The exact mechanism by which punc- turing proceeds is not clearly under- stood, due in part to the fact that our knowledge of molecular physics is con- fined largely to liquids and gases. The dielectric strength is given as the small- est potential necessary to cause a rup- ture. Heat plays an important part in this factor, as most materials have a positive temperature characteristic, and any rise tends to lower puncturing strength.
Most insulating materials are not absolutely homogeneous and therefore may allow minute leaks to start in an ad- vantageous path through the cellular structure. • The power loss in such a small leak may not be noticeable, yet the heat generated is concentrated in the minute path traveled and the fault develops cummulatively until puncture results. A condenser will therefore stand an excessively high voltage for a short period and yet sustain only a much lower voltage for a long period; this fact provides the basis for the standard two-voltage test for rating purposes.
Dielectrics have a hysterisis* charac- teristic which is similar in some respects to the magnetic hysterisis of iron and
produces a loss in the form of heat. The dielectric molecules and the few free electrons present tend to orient themselves under the influence of the plate potentials, therefore the rapid changes imposed by a.c. create an in- ternal temperature rise which in the audio range of 10 kc. or less is small, but in the radio frequencies may reduce the safe working voltage to 1/3 or ^4 of the normal d.c. voltage.
Inherent Condenser Losses
From the arrangement of Fig. 2 it is but a step to the arrangements used commercially, as shown in Fig. 3. When paper is the dielectric the form is of long strips of foil and paper wound in a shape of 3A, while with mica or glass the pile arrangement of 3B is used. These processes are carefully handled and the whole assembly sealed in a con- tainer with a non-hygroscopic wax. Small mica condensers are often com- pletely encased in moulded bakelite, which gives a unit impervious to atmo- spheric conditions and of an extremely low power factor.
A condenser is not a perfect storer of electricity but has various losses which for analysis may be grouped and considered as a series resistor, Rl of Fig. 2B. This resistance, which should not be confused with the capacitative reactance in ohms of the condenser, rep- resents the dielectric hysterisis loss, the loss from ohmic resistance of the plates and other lesser factors. Another loss due to leakage of the applied EMF through the dielectric is represented by the shunt resistance R2 of Fig. 1C.
A theoretically perfect condenser has a current leading the voltage by 90°, but all practical condensers have a lead of something less than 90°, depending upon the magnitude of the losses. This angular difference, ex- pressed in per cent, is called power factor, hence is a measure of the relative
and the electrolytic type 5%. At higher frequencies the losses and the power factor rise sharply on all types, and at ultra-high radio frequencies mica or one o(. the newer "synthetic" dielectrics must be used. The higher power factor of the electrolytic type is no objection in their use for power supply and many radio and amplifier applications. For example, the 8mf-450 volt unit, of which three might be used in a power pack, would give a shunt leakage of less than 3 milliamperes, which is negligible for this purpose.
The Electrolytic Condenser
An entirely different type of condenser and one which has the widest use in radio is the electrolytic. While the prin- ciple is not new (it having been known in the 17th Century that platinum elec- trodes immersed in a solution of sul- phuric acid gave capacities as high as 10 mf per square centimeter at voltages in the order of two) it is only in the last decade that any wide use of it has been made.
Some metals, such as aluminum, mag- nesium, and tantalum, when acting as the anode or positive plate of a con- denser in the presence of a suitable electrolyte, exhibit a polarization due to a film formed on the surface. This film is a polarized non-conductor and is believed to be composed of a layer of the metallic oxides along with occluded gases; because of the extreme thinness in the order of four one-hundred thou- sandths to four ten-millionths of an inch (this lesser value holding for a low- voltage type formed at 30 volts) tremendous capacities may be had in a small space.
About 1.16 mf per square inch can be had on a plate formed at 30 volts, which is one thousand times greater than a comparable paper condenser will afford.
The basic type consists of a liquid-
FIGURE
3
efficiency or "goodness" of a given con- denser, a low per cent being the desired goal. Paper condensers have power factors in the order of 2%, mica .08%,
*In physics, the lagging or retardation of one or two related forces or phenomena on ac- count of some change taking place in the medium through which they act.
tight copper or aluminum can used as a tank for the electrolyte in which is im- mersed the electrodes suspended by an insulating cover or stopper. Various electrolytes are used, the most common being an aqueous solution of ammonium borate or sodium borate (borax) and
INTERNATIONAL PROJECTIONIST
some boric acid, while with tantalum electrodes dilute sulphuric acid is used. Inasmuch as the cathode or negative
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100 200 300 400 500 600 Applied Voltage
FIGURE 4
electrode acts only as a contact with the electrolyte it may be used as the con- tainer, a common form being a can with three anodes, the can acting as the com- mon negative in the filter circuit.
During manufacture the anode must be "formed" by building the initial anodic film across the potential at which the condenser is supposed to operate, the capacity per unit area depending on the film thickness, which is a direct func- tion of the forming voltage. For ex- ample, an 8mf unit formed at 450 volts may have as high as 35 to 40mf when formed at 100 volts. This anodic film is a dielectric as long as the anode re- mains positive; when a negative poten- tial is applied the film breaks down and the condenser is practically short-cir- cuited.
This film also has a definite punctur- ing strength to a voltage in the normal direction, which, when exceeded, causes a breakdown that is automatically re- paired when normal voltage is resumed.
Compared with paper, oil, or mica condensers, there is considerable leak- age in the electrolytic type which in- creases sharply when maximum voltages are reached (as shown in Fig. 4) but normally it is in the order of .2 milli- ampere or less per microfarad. Thus is provided a safety valve for line voltage surges and to act as a shock absorber in the warming-up period in radios and small amplifiers by deliberately design- ing heavy shunt leakage at the region of maximum voltage.
The capacity varies directly with the temperature, giving a characteristic which may reduce an 8mf unit at 72° F. to as low as 4mf at 32° F. In the range of ordinary operating temperatures this effect is negligible. The leakage, power factor, and capacity all tend to change with age and other results of use, but these objections are far outbalanced by the great economy in cost and size over all other types.
A further reduction in size is obtained in the so-called dry type in which the electrolyte is carried by a layer of gauze
or other absorbent material wound be- between the foil plates. The anode film forms in the same manner as in the wet type, and the whole unit may be sealed in a wax board container which permits operation in any position.
The principle of increasing the effec- tive anode area by etching the electrode surface and thereby raising capacity with no increase in materials or size has further reduced bulk so they may be used almost anywhere in a chassis for by-pass purposes. The development of the dry electrolytic to the present state of reliability with extreme high capacity and very small bulk is a feat of labora- tory research and manufacturing re- sourcefulness.
Hints on Test Procedure
Previously in this article it was in- timated that condensers offered many elusive problems: frequently it may be advisable to go right through an ampli- fier and replace all the smaller con- densers, good or bad. At the present time the technician and projectionist have at their command several devices which go a long way to insure satisfac- tory tests. Fig. 5 shows two impedance biidges which will measure capacity, leakage, and power factor. The bridge on the left has a range from .00001 to 70 mf; the other runs from .00001 to 100 mf ; both use a 6E5 electric-eye tube as a balance indicator. These ranges do not include the low-voltage capacities used in A power and exciting lamp sup- ply units, which may be tested by the voltmeter-ammeter method. This method, however, involves heavy cumbersome equipment which is unsatisfactory for use outside the laboratory. The writer knows of no existing small portable test device for this purpose.
In replacing electrolytics which are
FIGURE 5
ing-up period. Smaller a.c.-operated amplifiers which have all heater-type tubes and a filament-type rectifier do not present a sufficient load when first turned on, because the rectifier filament builds up emission faster than the load and thus may present a dangerously high transient voltage.
To observe this, disconnect all filter condensers and place a 1 mf paper con- denser at the filter output and a high- resistance voltmeter at the filter input. The maximum swing should not exceed the surge voltage given on the condenser label. It can be shown experimentally that under conditions of no-load the out- put of a rectifier approaches the peak voltage of the impressed a.c.
A useful device with which to explore an amplifier chassis consists of an 8 mf tubular electrolytic with a probe and flexible lead connected to the condenser case, while the anode connector serves for the other probe. By using this as a temporary substitute capacity an open filter unit or source of hum may be shown; however, it will not reveal high leakage or shorts.
Examples of Application
With the recent increases in power and frequency range of sound picture repro- duction brought about by such advances as push-pull recording, high-resolution film, ultra-violet recording, the general reduction of background levels, and, most important, the improvement in horn sys- tems, the demands on an amplifier are more rigorous than ever. The db gain must be larger, the background levels lower and the frequency, amplitude, and phase distortion held to new lower levels.
The introduction of negative feedback has in one stroke reduced these distor- tion factors to a degree never before possible, but does so at the cost of gain. With this need of increased gain the in-
continually failing in filter circuits the stability through regeneration and inter- surge voltage should always be checked stage coupling increases tremendously, to make sure that the condenser maxi- which can be controlled only by elabo- mum is not exceeded during the warm- (Continued on next page, Col. 1)
February 1938
INTERNATIONAL PROJECTIONIST
17
New Simplex E-7 Projector A Great Advance in the Art
SIMPLEX E-7 is the name of the new and, in several respects, radically dif- ferent projector mechanism just intro- duced by International Projector Corp. as the first fruit of a widespread develop- mental program which is expected to be rounded out soon with the production of a Simplex 16 mm. sound projector and a completely new theatre sound system of exclusive International design from soundhead to horns.
The E-7 projector is now on sale at National Theatre Supply Co. branches throughout the country. The Super Sim- plex mechanism will of course continue to be produced and sold.
On pages 18 and 19 of this issue is a pictorial presentation of the E-7 projector which includes those units considered to be of particular interest to the practical projectionist, thus there is given here only a brief summary of the E-7 highlights. Units of this new mechanism will be de- scribed individually and in detail in future issues of I. P., a program which will be assisted materially by suggestions and questions from projectionists.
The Simplex E-7 is designed to meet the most exacting demands of a quality- conscious audience. New picture steadi- ness, freedom from blurring caused by oil stains, a.nd more light because of revolu- tionary shutter design, are some of its advantages. It needs less maintenance than any previous model, for the better quality of its screen image is derived not from mere refinements of construction but from inherently better projection arising out of improved basic design. In conse- quence the E-7 will retain its superiority through a longer period of peak perform- ance than any ever known. Moreover (and perhaps most important of all) new conveniences of operation rid the projec- tionist of small obligations of routine and leave him freer than he has been to concentrate on screen presentation.
An automatic, one-shot lubricating sys- tem assures that every bearing receives a precisely metered quantity of clean, filter- ed oil. None can be forgotten or over- looked. None takes the eye or mind of the projectionist away from his screen. And there is no surplus of oil to spatter the film compartment and soil the image.
The intermittent movement operates
rate by-passing and isolation of the stages from common impedances by ade- quate filtering.
A representative stage of amplification, illustrating the importance of con- densers, is given in Fig. 6, in which a screen grid tube is resistance-coupled to the following stage. The capacity Cc provides a low common impedance fcr both the grid and plate circuits across the bias resistor, which otherwise is a common impedance of about 2,000 ohms. In earlier practice this would be
reactance be less than the resistance which it shunts.
The characteristics of Cb, the coup- ling capacity to the following grid, are very important as the size of this con- denser determines the low-frequency cut- off and therefore the bass response. It must be large enough to provide low re- sponse and yet must have extremely low leakage to prevent the positive potential of the preceeding plate circuit from affecting the grid. Other things equal, leakage increases with capacity, and as a result, for condenser Cb a good grade of paper or mica must be used.
The two networks at the lower part of Fig. 6 are filters which reduce the feedback signal (not to be confused with negative feedback for corrective pur- poses) from the common interstage im- pedance of the power supply to values lower than the overall gain of the ampli- fier. To accomplish this the capacities of CI to C6 must be large enough to have a low impedance as compared with
with a wholly new smoothness and free- dom from vibration, the result of an oil cushion introduced between star and cam. Far closer tolerances are thus made pos- sible. Every show during the life of the mechanism benefits through increased screen steadiness. Every part of the pro- jector and sound head wears longer through reduction of vibration.
The new governor is of the ring-type of construction, trouble-free, bind-proof, and absolutely silent in operation. The drive gears are oversize, and the transmission gears are helical in design. No amount of wear can make the new synchroniz- ing device produce travel-ghost.
Side sway of the film is controlled by replaceable guides, spaced with micro- scopic accuracy, which act in conjunction with the guide rollers. Irregular loss of picture steadiness is prevented by an ex- ceptionally long pressure pad combina- tion, which exercises complete control over the film from the intermittent sprock- et to a point far above the aperture. Double shutters — front and rear — inter- act to give more light, a sharper image and far less eye-strain. The automatic, free-falling fire shutter is positive in ac- tion and prevents aperture fires under any circumstances whatever.
White, illuminated interior facilitates threading, makes dirt plainly visible and therefore more promptly removed. The special framing lamp minimizes the chance of the picture appearing out-of- frame on the screen, regardless of the darkness of the print. (See pages 18 and 19) .
-J— /-.«-. ^- r\i -^- <"■/! ~*~ r>R r>A
C5 -p C6 -r-
FIGURE 6
-5 mf, but with the dry electrolytic type 5 to 20 mf is used, which actually ful- fills the requirements that the capacity
the resistance they shunt, thus offering a virtual short-circuit to ground of the harmful feedback.
THE PROPER USE OF ILLUMINATION TERMS
Appended are excerpts from a discussion of illumination terms by Messrs. G. H. Stickney and E. C. Crittenden which appeared in the ''Transactions of the Illuminating Engineer- ing Society" (Feb., 1938, Vol. 33, No. 2).
SEVERAL instances of inaccurate us- age center around the . . . term "il- lumination." The Society has defined "il- lumination" as "the density of luminous flux on a surface ..." The most com- mon unit of illumination in this country is the "foot-candle." This might be re- ferred to as a quantitative meaning. While the Society does not so define it, it is obvious that illuminating engineers, in common with laymen, also use "il- lumination" in a qualitative sense to de- note a process or, as the dictionary puts it, the "act of illuminating" or "state of being illuminated."
Some technicians, conscious of the two meanings, doubt . . . that "illumination" connotes the quantitative meaning of the I. E. S. definition, and so they look for a substitute or an explanatory expression ... It appears that . . . where one of these expedients is resorted to, the sense would be absolutely clear without it. For example, "illumination of 20 foot-can- dles," "more illumination," "higher il- (Continued on page 33)
The New Simplex E-7 Projector: M
Synchronized Front and Rear Shutters. Advan- One-Shot Oiling System insures positive lubrica- Intermittent Oil System preven I
tages are: constructional; increased screen illum- ination; better picture presentation due to dis- solving effect; single heavy shaft for mounting both shutters; avoids slight misalignment caused by rough handling in shipment.
tion to all bearings as required, eliminating possi- bility of failure, as on previous models. Oil is filtered, thus insuring a clean supply in sufficient quantity at all times.
oil overflows on drive side. Res $ Oil cushion under pressure beti I closer tolerance and shock ah / tion reduction ant
Ovetsize Drive Gears revolving on fixed studs insure longer life and simplify maintenance. This type gear places pressure of operation where it causes least wear. On repair jobs re-bushing of main frame is eliminated.
Rear Shutter Guard design permits easy removal of the guard without interfering with setting of the arc lamp and its optical •system. Previous models required movement of lamphouse for necessary shutter adjustments.
Framing Lamp, operated by fir, I positions directly behind aperi curate framing regardless of p. Box of baffle construction int heat consistently throughout dr able without to,
Film. Trap is almost instantly removed, assuring easier accessibility for cleaning and adjustment. Contrast this construction with previous models. See close-ups of trap and gate; also, see removal of gate.
Ring-Type Governor Control for Fire Shutter. This unique type of control, which operates on the principle oj a gyroscope, eliminates the pos- sibility of a bind-up and is silent in operation.
Shutter Synchronizing Device a up wear in shutter assemblies, vious models was reflected in impossible in this new E-7 de continuously sharper
rraphic Story of Its Main Features
<i'ge on operating side. Excess fin be refilled from either side. In ring and star wheel permits J, insuring longer wear, vibra- nsed steadiness.
Automatic Fire Shutter Safety Trip provides posi- tive protection against aperture fire by auto- matically cutting off the light from the film by releasing the fire shutter when film remains sta- tionary before aperture plate.
Film Gate is almost instantly removed, assuring easier accessibility for cleaning and adjustment. Contrast this construction with previous models. See close-ups of gate and trap; also, see removal of trap.
r lift lever, \ suring ac- \isity. Sight i, disburses \iily remov-
Film Gate Guide. Gate wobble has been elimin- ated, regardless of length of service, by inter- action of four parallel opposing surfaces. The gate is controlled by a flat-sided guide stud, with adjustments for wear.
'cally takes Rear Shutter Cooling Fins. Newly designed con- iear in pre- struction of blade and curved vein draw the air n. ^ This is backward from aperture and pass it around out- « insuring side of mechanism, insuring much cooler film path than was possible heretofore.
Improved Film Gate. The in- creased length of the Pressure Pad combination, together with the Spiral Spring and Adjustable Tension devices, insures that the film will be held in the proper position against the Film Trap with the least amount of tension necessary for the various types of film that may be supplied: namely, oil and shrunk film, un- processed film and new film. The film is also controlled accurately from the Intermittent Sprocket to a point far above the Aper- ture, insuring a far steadier pro- jected image.
New Type Film Trap construc- tion. To further insure the ut- most steadiness of the projected picture, the Film Trap design in- cludes, in addition to the regular Guide Rollers heretofore used to control side sway, replaceable guides spaced with absolute ac- curacy. These guides act in con- junction with the guide rollers aforementioned and prevent side sway of the film such as was pos- sible on all earlier models. See close-ups of almost instantaneous removal of both film gate and trap.
The New Simplex E-7 Projector: A
Graphic Story of Its Main Features
nl Front and lie imul ;
Shutters. Ativan- i'il screen ilium-
SyncUr
tttges «...
Inalloni hotter picture premutation due lo ttut
lolving effect: single haavy «"«/' for mimnting
bmh thulterti avoids flight misalignment causal
ov rmiuh Uanilling ill «7lipm(MI.
One-Shot Oiling System insures positive lubrica- tion to all bearings as required, eliminating possi- bility of failure, as on previous models. Oil is filtered, thus insuring a clean supply in sufficient quantity at all times.
wm
Intermittent Oil System prevents leakage on operating side. Excess oil overflows on drive side. Reservoir can be refilled from either side. Oil cushion under pressure between leant ring and star wheel permits closer tolerance and shock absorptimn, insuring longer wear, vibra- tion reduction and increased steadiness.
Automatic Fire Shutter Safety Trip provides posi- tive protection against aperture fire by auto- matically cutting off the light from the film by releasing the fire shutter when film remains sta- tionary before aperture plate.
Film G,
nil,
stantly removed, assuring
easier accessibility for cleaning and adjustment.
Contrast this construction with previous models.
See close-ups of gate and trap; also, see removal
of trap.
Ovottlno Drive dear* revolving on fixed studs insure longer life and simplify maintenance. This
type gear places pressure of operation where it Cantos least wear. On repair jobs re-hushing of
main frame Is eliminated.
Rear Shutter Guard des:gn permits easy removal of tile guard without interfering with setting of the arc lamp and its optical system. Previous models required movement of lamphouse for necessary shutter adjustments.
positions directly behind apet g
curate framing regardless of J>»» , «.gft
Box of ^ffle constructmnf >ky *«- heat consistently througnw ,
Film Gate Guide. Gate wobble has been elimin- ated, regardless of length of service, by inter- action of four parallel opposing surfaces. The gate is controlled by a flat-sided guide stud, with adjustments for wear.
Trap is al easier accessli
Contrast tin See
» a moil instantly roi ,.,|. „ss„r,„„ R(n..T¥no r
ub.hty for clenn ng and ml;,.,,,,.,,,,. j7llsS J-?* C°Mrnof CoT"ro1 *>r F™ Shutter. Shutter Srnchron trust this coMlruclIra wltj. pre.iou. moid., hTorlT, "T of con«»l' >°>»ch operates
close-ups of ,raP and gate: also, see „„„, K4*J* °> « Bioscope, eliminates ,t
■asSS*-
— j pos- silent in operation.
<t' assemble %k*r tV^ shutter ass' . ;„ W , • . Th,t ;s
h .vas reflect* ^ifi^*' .«,„„•„
m this no**' ,*•?*"■
up wear tn
vious models «>«» "' g,m impossible in this nev <ftflrp£J continuous1?
Rear Shutter Cooling Fins. Newly designed con- traction of blade and curved vein draw the air acktcard from aperture and pass it around out- e of mechanism, insuring much cooler film path than was possible heretofore.
Improved Film Gate. The in- creased length of the Pressure Pad combination, together with the Spiral Spring and Adjustable Tension devices, insures that the film wilt be held in the proper position against the Film Trap with the least amount of tension necessary for the various types of film that may be supplied: namely, oil and shrunk film, un- processed film and new film. The film is also controlled accurately from the Intermittent Sprocket to a point far above the Aper- ture, insuring a far steadier pro- jected image.
I\ew Type Film Trap construe* tion. To further insure the ut- most steadiness of the projected picture, the Film Trap design in- cludes, in addition \o the regular Guide Rollers heretofore used to
control side sway, replaceable
guides spaced with absolute at- curacy. These guides art in con- junction with the guide rollers aforementioned and prevent side sway of the film such as was pos- sible on all earlier models. See close-ups of almost instantaneoun removal of both film gate and trap.
The Place of Television
Among the Visual Arts
By DR. A. N. GOLDSMITH
CONSULTING ENGINEER, NEW YORK CITY
This is the third article of a series covering recent technical developments in television and charting the future of the art. Written by acknowledged authori- ties on the subject, this series should prove of great value to those interested in the progress of this baby art — as are most projectionists. This article originally appeared in "Television" (Vol. II), published by RCA Institutes Technical Press, and appears here through the courtesy of that organization.
THE new field of television is under rapid technical development and program study. It is reasonable to expect that it will soon be one of the major visual arts, with a technique of its own and with broad applications of great public interest and commercial significance. Accordingly, it seems ap- propriate to attempt to classify tele- vision among the visual arts, to study its relative advantages and disadvantages, and to attempt to judge some of its specified capabilities and limitations.
The other major visual arts are, of course, direct ocular vision, as accom- plished by all of us through our eyes, and the arts of still-picture and motion- picture photography. We need not con- sider here still pictures. It is necessary for our purposes to compare television only with human vision and with motion picture processes.
It seems that television is a curious and rather unexpected blend of direct vision and motion-picture photography. It lies between these two older fields, borrowing from each and perhaps adding its own contribution. It seems worth while to compare these arts more speci- fically in various basic respects.
Duration of the Image
The first element meriting considera- tion is duration of the envisioned picture. In the case of direct vision 'the image is completely transient. If we humans were not equipped with memory, our eyes would be of little use, since it is not the eye but the brain that remembers. While it is a convenience to be able to shift our vision from one subject to another, yet it also places us under the handicap of having to retain a vast store of mental images or visual memories.
The motion picture, on the other hand, is a recorded and practically permanent pictorial record. Subject only to the limited factor of physical life of film, a motion picture can be viewed at any time in the future in its original form. The silver image in the emulsion on the
film is, in fact, nothing more than the stored memory of previous happenings.
Television, oddly enough, is either transient or permanent, depending on its mode of use and the extent to which it utilizes its allies, the motion picture or, alternatively, the electrical record. If we have a direct television pick-up in- stantly transmitted to the usual cathode- ray receiver in the home, television is as transient as direct vision. But suppose that at the transmitting station or the receiving station we record the pictures. This can be done either by the usual motion picture process or, theoretically at least, we might record the electrical variations at transmitter or receiver which correspond to the video modula- tion and the picture controls (such as synchronizing and background cur- rents) . In this way we can have either a film record or an electrical record of a television presentation and thus provide a "television memory."
Considering next the element of color, direct vision is, of course, color vision (except for the unfortunately color-blind individuals). Motion pictures similarly can be either monochromatic or in full color, though the latter process is riot too readily accomplished. Television, in
theory at least, can also be either mono- chromatic or in color. Nevertheless, color television at this time presents a most forbidding aspect to the already sufficiently harassed television experi- menter and designer.
Sensitivity of Various Processes
As regards the sensitivity of the vari- ous processes, direct vision has an ex- tremely high sensitiveness to light and is limited only, so far as we know, by the sensitiveness of the electro-chemical effects occurring at the retina of the eye. Where the sensitivity of the eye is un- comfortably low, we either increase illumination or perhaps use such auxiliary light-gathering devices as the telescope (and ultimately perhaps, the electron telescope with its capabilities of amplifying light). So far as motion pictures are concerned, the process starts with the formation of a latent image, and again is limited by the sen- sitiveness of an electro-chemical process.
Film may be specially sensitized, illumination may be increased, or some other equivalent measures used if or- dinary film sensitivity is found to be in- adequate. Television is also limited by an electrical characteristic in its sen- sitivity, namely, by the sensitivity of the photo-electric effect. It is possible greatly to amplify the output of the original photo-electric pick-up device in television by such means as the secona ary-emission amplifier. It is also pos- sible, within limits, to increase the brightness of illumination of some sub- jects for television. However, consider-
The television receiver, with its reflecting mirror in the lid of the cabi- net; and the 3 x 4-foot screen upon which the image is pro- jected
[20]
THE ONLY WAY TO HOLD YOUR PATRONAGE...
THE STRONG MOGUL
is by taking advantage of the improve- ments in modern equipment:
Theatregoers today expect highest qual- ity projection. They've been made accus- tomed to it by the high intensity equipped theatres which constitute three-fourths of America's seating capacity.
Good color projection demands two to three times as much light— the snow white light provided by high intensities. *
Projection with Strong Moguls is not a luxury. It actually costs less per light unit than old style low intensity.
Write today for interesting catalog and name of your nearest Independent Theatre Equipment Dealer.
1L
STRONG ELECTRIC C
Ctp.
f
2501 LAGRANGE ST. TOLEDO, OHIO, U. S. A.
EXPORT OFFICE: ROOM 2002, 220 W. 42nd ST. NEW YORK, N. Y.
it
diet
topecuau
SIMPLIFIED
PROJECTION
22
INTERNATIONAL PROJECTIONIST
February 1938
ing the electrical background of each of the three visual methods of pick-up, it is not astonishing that their sen- sitivities are of the same general order of magnitude.
The range of transmission or viewing is quite different in the three cases in question. So far as direct vision is concerned, this extends optically to the nearest opaque obstacle, which may be anything from the walls of a room or the horizon to the furthest regions of the universe. Visual range is </