Reel and Slide (Jan-Sep 1919)

REEL and $ L I D E 25 k Projection it Edited by M. BERNAYS JOHNSON (Projection Division Westinghouse Lamp Company) Questions on projection will be answered by this department provided addressed and stamped envelope is enclosed. Address Projection, Reel and Slide Magazine, 418 South Market Street, Chicago, 111. !ll!llllll!lllllllllllllllllllllilllllilll!lllllll!ll! SPROCKET TEETH AND FILM PERFORATIONS Among the further subjects that merit careful attention by the Society of Motion Picture Engineers, there are probably none which 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 the means for the prevention of the side vibrations 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 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 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 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 from time to time due to atmospheric changes and moisture treatment it is not practicable to undertake to guide the film by having the teeth on both sides of the sprocket wheel the same length as the perforations of the film. Therefore, it seems necessary to make the teeth on one side of the sprocket wheel to fit closely the length of the film perforation and then shorten the teeth on the opposite side sufficiently to allow ample freedom for expansion and contraction in the width of the film. At a recent meeting of the society, the consideration that preceded the adoption of a standard for film perforation presented some complications because of the expected future relationship between the film perforation and the form and size of the sprocket teeth, and of finding a practical means for producing the film sprocket. It was the belief of some of those present that the use of a film perforation with circular ends would present complications in the forming of the sprocket teeth to fit the perforations that might be so great the plan would not be practical, and that teeth made to fit a rectangular perforation with rounded corners would eliminate the complications in manufacturing, make it possible to grind both the ends and the sides of the sprocket teeth, thus correcting both the alignment and the spacing of the teeth, and would make it possible to secure the greater degree of accuracy in the projection of the picture on the screen. Mr. Bell, of the Bell & Howell Company, of Chicago, stated that for several years past they have been using on their film printers, sprocket wheels with teeth on one end made to fit the perforations in the film to prevent side movement, while the teeth on the other end of the sprocket wheel are made shorter. This plan has been possible with them because usually the film manufacturer who uses their goods adopts their equipment complete, including film perforators, cameras, printers, etc. Mr. Bell said they have been "forming" the teeth of the sprockets for their film printers, but that the method they are using for "forming" the teeth would probably not give satisfactory results in the production of a sprocket wheel of small diameter, such as is used for projection work. He said, however, they have given some thought to a method of "generating" the teeth that would be suitable for the production of sprocket teeth on a commercial basis with a sufficient degree of accuracy for practical purposes, and having in mind the present almost universal use of the film perforations with the circular ends, and the almost unsurmountable difficulties in the way of undertaking to get the manufacturers to change the form of teeth they are at present using largely because of the great amount of expense involved in changing their machinery, cameras, etc., the society thought best to adopt the film perforation with the circular ends. * * * In making the teeth with ends formed by their present process, as shown in the accompanying drawings, a hollow mill or forming cutter is used. The mill operates through a bushing to center it, for the prevention of vibration and to make it possible to cut on only one side of the center. The sprocket wheel should be indexed for each tooth the same as in the regular operation of cutting the teeth on a gear cutter. The opening in the end of the cutter used for forming the teeth is made conical to fit the form of the teeth. — From an address delivered before the Society of Motion Picture Engineers, by A. E. Roebuck. PROJECTORS Used and 'rebuilt and brand new motion picture machines at half regular price. Power, Motiograph, Edison and other makes for electric, Mazda or calcium light. Single and dissolving stereopticona and one brand new Baliopticon. Bargain lists covering everything in the business. FREE. NATIONAL EQUIPMENT CO., Duluth, Minn. PLAIN TRUTH ABOUT SCREENS Some plain truths about moving picture screen quality come to this department from the Minusa Cines Screen Company of St. Louis, makers of the famous Gold Fibre screens. We read: "It's ridiculous to buy a screen, particularly one for perfect projection, for less money than you know it costs to build a good one. The 'cheap screen' manufacturer must make a profit, and the only chance he has in such a transaction is to lower the quality of his product. You know this to be true; you know a screen built of cheap material can not 'stand up' mi give the same satisfaction that a screen built of the very best material can. "The Minusa Gold Fibre screen is a scientifically designed screen, it is constructed by the most efficient workmen ten years have been able to assemble, and it is made of laboratory-tested material — the finest quality money can buy. Each Minusa Gold Fibre screen is built to fit the auditorium in which it is to be used. This accounts for the variations of surface and color requisite to conform to the different specifications; no two Minusa Gold Fibres are constructed alike, unless the dimensions of the rooms are identical. "Now, think, just for a moment: Does it stand to reason that a screen surface 12x16 ft., producing perfect results at 150 ft. on D. C, would produce the same results on A. C. at 100 ft. on, say, a 9 x 12 ft. picture? The color characteristics and nature of A. C. and D. C. light are essentially different. The size of the picture and length of throw are different. "Shouldn't the screen be different, as well?" What is the best kind of a projector for class room work? L. K. Answer: That depends on what line of work you want to do. If your school has an auditorium, you do not need a portable; if you want to move the machine from room to room, the portable is best. There are many reliable makes. Consult the advertisements in this issue. * * * WIRING THE SCHOOL FOR MOVIES In most of the larger American cities, new school houses are being wired for motion pictures even in cases where there is no provision made in school funds for projection machines, screens or other necessary equipment. A great saving is possible by utilizing this beforehand method and it is safe to say that it is being generally adopted all over the United States. In rural districts where adequate current is not readily available, small power units are made to serve this purpose, but even in a case like this, auditorium wiring at the time of building is well worth while. In Ohio, quite a number of new rural school houses are being built and, in nearly every case, the necessary wiring is being done at the time of construction. This also holds true of many Methodist and Catholic churches in the Middle West. It would be best if school boards generally adopted this as a policy — to allow a certain fund for wiring the buildings as they are planned and to include this automatically in the budget of costs for each new structure. As it is only in recent years that the school house has been found useful as a community center and therefore needful in the evening, the average lighting facilities are very poor. Quite a number of readers write this department that they must resort to an automobile or a farm truck in order to secure current when showing films in country school houses away from the cities and towns. It is pretty generally agreed that every school house of the future will include in its equipment modern projection facilities. This being the case, the educators should not close their eyes to the value of giving this equipment a fair chance by insuring adequate current beforehand. * * * How can I change my carbon outfit for Mazda light? I have a Powers machine. H. J. Answer: There are two adapters on the market. One is furnished by the Precision Machine Company, New York City. The other by the Motion Picture Projector Company, 35 South Dearborn street, Chicago. * * * What is the "throw" of the average portable projector, like the De Vry? Simmons High. Answer: Most high grade machines make possible a throw of 80 feet. * * * What causes extraordinary flicker on the screen? B. K. L. Answer: Usually, the image impressed upon the film is not exactly in line with the divisions indicated by the sprockets. This may cause unsteadiness. Have your project adjusted. COLD FIBRE SCREENS MINUSA MAZDA-LITE SCREENS A special creation for Churches, Schools, Lodges, etc., made in sizes to suit your requirements. Distributors from Coast to Coast Samples and information upon request INUSA CINE SCREEN CO. WORLDS LARGEST PRODUCERS OF _, : MOVING PICTURE SCREENS. [gglSJSg]] Bomont and Morgan St. Louis, Mo. |EJ>