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A FILM FOR MEASURING PROJECTOR STEADINESS* M. G. TOWNSLEY**
Summary. — A film is described which has circular perforations in each frame which are punched after exposure and processing of the film. The perforations in each frame are located from the normal film perforation and from the edge of the film which is guided during projection. The modification of a standard Bell and Howell perforator for producing this film and a method for checking the accuracy of the finished film are described.
Steadiness in a motion picture projector is the ability of the film moving mechanism to place successive frames of film in the aperture in such a manner as to cause the images in each successive frame to occupy the same position on the screen. Sixteen-mm projectors locate the film frames vertically from a perforation and laterally from the edge opposite the sound track.
A film having an image in each frame located vertically from the same perforation as is used in the projector and laterally from the guided edge may be used to measure the steadiness of a projector, provided that the location of the image is performed with sufficient precision. This could be conveniently accomplished by perforating a pattern in each frame at the same time as the film perforation in the raw stock. There are, however, certain disadvantages in this method. In the first place, it is usual to perforate several frames at the same time when punching raw stock. This introduces possible systematic errors in the film perforation and makes it necessary that the multiple punches required to perforate the steadiness pattern each be accurately located witih respect to the corresponding film perforating punch. The possible systematic errors in perforation of the raw stock and possible variations in punch sizes make it desirable to produce the steadiness test pattern one frame at a time, locating always from the same side of the perforation as will be used in projection and from the guided edge.
* Presented Apr. 19, 1944, at the Technical Conference in New York. ** Bell and Howell Company, Chicago, 111.
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