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tight then film wear is increased with possible tearing of film and interruption to service.
We have been informed that adjustable tension is necessary to compensate when using old or new film. With the slow intermittent our results have indicated satisfactory performance on all film tried with no variation in adjustment at all. With the fast types this was not the case and adjustment for new and old film was necessary. Soft new film having a higher coefficient of friction, of course required less tension on the shoes to accomplish their function as explained. Shoes set for old film tore new film, and those set for new film allowed picture jump with old. It seems then that deficiencies in design of the intermittent are compensated by adding an adjustable device which requires very critical adjustment by the operator for each kind of film run to insure entirely satisfactory service.
The foregoing are some of the reasons why we feel convinced that, for our purposes, only the 90° Geneva Star and Cam will meet the requirements. This intermittent which has been previously referred to as the 1 to 1 based on ratio of star and pin circle diameters is the same as is sometimes referred to as the 1 to 3, based on the ratio of time of moving to the stopped periods per revolution. It is hoped no confusion will be introduced by the phraseology used.
Closely connected with the intermittent problem in the quality of projection and film life appears the sprocket design. This seems to have been pretty well worked out by the Eastman Kodak Company, on the standard film perforation, considering film shrinkage, etc.
However, our tests have revealed no machine submitted which actually followed the data of the above named company in their sprocket design.
The length of the arcs of film contact on the various sprockets does not seem, in general, to have received much consideration and certainly no standardization. One make only appears to have given it consideration really worth while.
The more teeth in mesh the greater will be the effect of the film change through shrinkage and unless this is compensated serious film damage seems likely to result.
It is hoped that the general question of intermittent design has not been too much stressed. It is not meant by this to convey the impression that many other things, such as framing, shutter design, sprockets, etc. are not thought to be of great importance in efficient projection. It is only that the intermittent is believed to be of the greatest importance for our purposes.
Commercially perhaps the cost of film is not greatly considered and the amount of film damage chargeable to a given design is not readily apparent. But unless film producers are running for charity, the operators must be paying the combined cost of an enormous amount of uselessly damaged film through increased film rental charges.
The automobile engineer did not, in the early history of the industry, consider to any great extent tire mileage nor the effect
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