International projectionist (Jan-Dec 1948)

unimportant, which as a rule receive no great attention by the projectionist. The result is that film trouble is likely to start at any one of them. The appended resume covers the more important points which must be given careful attention by the projectionists if the maximum wearing qualities are to be obtained from the film. Tension in Springs in Gate or Trap — One of the principal sources of trouble is excessive tension exerted on the film by the springs in the gate or trap. A great variat on will be found in tension on various projectors being used. Moreover, some projectionists are not familiar with the amount of tension which should be used. As far as is known, there is no generally accepted standard. The tension springs should be set just tight enough to hold the film stationary at the aperture. This adjustment provides conditions for a steady screen image. The proper pressure will of course depend on the projector used, the length of time it has been in service, and the type of surface treatment the film has received. Tension in excess of this amount merely results in added film wear. The pressure on the film should be exerted evenly on both edges to prevent an unequal pulldown strain. The proper method of making a tension test is illustrated in Fig. 1. First, the tension on one side and then on the other is taken by using one half of a strip of film about 8 inches long. This strip is prepared by slitting a piece of new film of average thickness down through the center. Care should be taken to observe that the perforations on this strip of film do not engage the teeth on the intermittent sprocket and are held properly in place by the tension shoe before proceeding further. The test should be made on a cold FIGURE 1 7 A. A spring bolonce graduated in ounces is convenient for tension tests. 6 (right) Tension tests are made on each side: 1 is the film, 2, the pressure plate, and 3, the spring balance. FIGURE 2 A tension test is then made on both sides: 1 is the film, 2 the pressure plate, and 3 the balance. projector to insure uniformity. After fastening the end of the strip of film to the balance, a straight, even, upward pull is made until the film just starts to move. Tension springs should be adjusted so that both sides are equal. The combined tension of both sides may be checked as shown in Fig. 2. A full-width piece of film is placed in the gate so that both sides of the shoe hold it firmly against the aperture plate. After making sure that the perforations on this strip of film are not engaged by the sprocket teeth, proceed as before with a straight upward pull until the film just starts to move. The majority of present-day projectors should give a steady screen image with comparatively low trap tension. Tests made over a long period in the Kodak Research Laboratories indicate that with most projectors a tension in excess of 16 ounces (a total of 8 ounces for each side) only increases the wear on the film. The design of some projectors permits satisfactory projection with as little as 6 ounces tension, so that a satisfactory range between 6 and 16 ounces is recommended; the amount of tension depends upon the projection equipment used. It is always advisable to test new projectors before film is run to make sure that the tension is not in excess of the recommended level. The tension springs on some projectors can be regulated by means of small setscrews. When no adjusting device is provided, the springs must be bent by hand and great care must be taken to make the proper adjustment, making certain that both sides are adjusted equally. Sprockets — Through carelessness and neglect sprockets are frequently left on projectors until the teeth develop bad hooks and knifelike edges. Film damage caused by undercut teeth is unmis takable in appearance, and in many cases film is practically ruined after one or two showings if it is run on a projector equipped with such sprockets (Fig. 3). An intermittent sprocket must be changed with great care, as the shaft can be bent very easily. This replacement should be made by someone thoroughly familiar with this type of work. In some cases it may be advisable to have the work done at the factory to insure the best results. Before new sprockets are placed on projectors, a careful examination should be made of the teeth to be sure that none of them have been damaged by coming in contact with one another or with some hard surface. If a sprocket is accidentally dropped on the floor, the teeth are likely to be burred, and if such a sprocket is used on a projector it may cause untold damage to film. This is true even if only one tooth has been damaged. Adhesion of Emulsion to Shoe or Film Tracks — All new film, unless previously lubricated at the laboratory, should be waxed or lubricated to insure against adhesion or sticking in the gate or trap of the projector. If new unwaxed film is run, it is necessary to clean the shoes frequently; otherwise the accumulation of hardened emulsion on the shoes acts as a holdback and causes a greatly increased pull-down strain, which always results in mutilated perforations. Needless to say, a new print can be completely ruined in this manner at one showing. In removing the hardened emulsion deposits from the film tracks and tension shoes, do not use a steel or iron implement such as a screwdriver, safety razor blade, or file. Use a damp cloth, or a moistened orange stick, or if necessary a coin, as this will not scratch the highly polished surface. Guide Rollers — The rollers located FIGURE 3 Sprockets are a prime source of film mutilation. The examples shown here were taken from projectors actually in daily use. Sprocket A is new. 8 INTERNATIONAL PROJECTIONIST • October 1948