The motion picture projectionist (Nov 1930-Oct 1931)

November, 1930 Motion Picture Projectionist 39 Film Mutilation (Continued from page 29) more of these points, it must be admitted that the direct cause of a great amount of film damage is never definitely settled between the film exchanges and the projectionists, especially when the projectors in question have been gone over quite carefully and everything has been found to be in apparently good condition. In cases of this kind, it is only natural to assume that the film stock is at fault. There are, however, various projector parts, generally considered more or less unimportant which, as a rule, receive little or no attention on the part of the projectionists. The result is that the film trouble is apt to start at any one of them. The following resume covers the more important points which must be given careful attention by the projectionist, if the maximum wearing qualities are to be obtained from the film. Tension on Springs in Gate or Trap One of the principal sources of trouble is the use of excessive tension exerted on the film by the springs in the gate or trap. A great variation will be found in tension on various projection machines being used in the trade. Moreover, there are some projectionists who are not familiar with the amount of tension which should be used, and as far as we know, there is no set standard which is generally accepted as being correct. It is common practice to set the springs just tight enough to hold the film stationary at the speed which is used in a given theatre. Excessive tension as high as 34 ounces has been XL f— ^" T Fig. 2A. A spring balance graduated in ounces is convenient for tension tests. Fig. 2B. Tension tests are made on each side. 1 is the film, 2 the pressure plate and 3 is the spring balance at S ounces. found to exist on certain projection machines and causes badly nicked and pulled out perforations. Heavy tensions on one side can be caused by a poorly adjusted, weak or broken spring and results in an uneven pulldown strain on the film. On projectors using the gate a stop or catch is provided which holds the gate in the same position each time it is closed. Projectors using a trap door or pressure plate are not provided with a stop of any kind, thereby allowing varying amounts of tension to be applied to the film. The trap door or plate should never be let back against the film with great force as this results in exceptionally heavy tension, which must be withstood by the film until the door or plate has worked back to its proper position. The proper tension exerted by the springs should be 8 ounces for each spring or 16 ounces combined tension. Below Figure 2 is given the proper method of making a tension test. Referring to illustration JB : first the tension on one side and then on the other is taken by using one-half of a strip or film about 8" long. This strip is prepared by slitting a piece of film down through the center. Care should be taken to observe that the perforations on this strip of film are free of the teeth on the intermittent sprocket and are held properly in place by the tension shoe before pro(Continued on page 44) BLUE SEAL HEAT RESISTING IMPROVED FILM TRAPS FOR SIMPLEX PROJECTORS MADE OF AN IRON ALLOY Guaranteed not to Warp under the intense heat of the Arc Spot. A necessity for the Perfect Projection of "Sound" Pictures B-16 Film Traps with Sliding Double Round Corner Apertures, one Aperture for Disc and Silent Film and one cut Proportional for Movietone Film to be used with our Adaptors.... $30.00 B-17 Sliding Double Aperture Plate 6.00 B-24 Film Trap with individual mats for silent, movietone and magnascope effect. Traps complete with all mats 30.00 B-20 Master Plate to hold mats stationary 1.50 B-21 Standard Aperture with Square Corners 1.50 B-22 Proportional Movietone Aperture with Square Corners 1.50 B-23 Blank Mat (CAN BE CUT ANY SIZE APERTURE).... 1.50 Manufactured by BLUE SEAL PRODUCTS CO., Inc. 262 Wyckoff St. Brooklyn, N. Y. Manufacturers of Motion Picture Accessories Since 1913