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SPROCKET TEETH AND FILM PERFORATIONS AND THEIR RELATIONSHIP TO BETTER PROJECTION
By A. C. Roebuck
Among the further subjects that merit carefulattention by the Society of Motion Picture Engineers, there are probably none that present greater possibilities than those that may lead to the elimination of as much as is practicable of the unsteadiness or jumping of the picture on the screen.
It was prior to 1900, I believe, that means for the prevention of the side vibration of the film became a question of importance. The first effort toward the elimination of this objectionable feature was the use of a guide for the edges of the film, the guide for one edge being made flexible, but this plan was found to fall short of expectations and it never came into general use.
To undertake to guide the film accurately by the sprocket teeth was not possible at that time because of the wide variety in the sizes and forms of film perforations in use. Film perforators in the early days were mostly made under the direction of the maker of the films and there was apparently no effort made toward the standardization of the perforations. The length and width (especially the length) of the perforations and the distance between centers across the width of the film were different with each manufacturer, and it was found as late as 1906, I believe, that one manufacturer used at least five different forms of perforations. I believe the first perforations were rectangular in form with slightly rounded corners. Later the present type of perforation with circular ends was introduced, as I remember it, by Pathe Bros., of Paris, France, and this type of perforation has gradually grown in favor until it is now almost universally used.
The former perforations of varying lengths and widths and of varying distances between the centers of the perforations across the width of the film, placed the manufacturers of projecting machines at a great disadvantage, not only in being unable to use the sprocket teeth as a guide to prevent side vibration of the film, but also the wearing qualities of both the sprocket teeth and the film were reduced because of the teeth having to be made so much shorter than otherwise would have been possible.
Now that the general use of a standard film perforation is apparently a near future possibility, it seems it will be possible to use the teeth on one end of the sprocket wheel as a guide to prevent side shake by making them wide enough to fit the length of the perforation as is being done by at least one of the manufacturers of film printing machinery. To obtain the best results, this plan would require that the teeth must be properly formed, not only on the ends, but on their sides from base to point in order to give the film proper clearance as it engages and leaves the teeth.
Owing to the shrinkage in the film due to the elimination of moisture, especially while new, together with its expansion and contraction
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