Motion Picture Herald (Jan-Mar 1956)

$425 FOB SEE YOUR THEATRE EQUIPMENT DEALER DAWO CORP. . 145 N. ERIE ST. • TOLEDO, OHIO *R€Ap mu^/' ping point. This may generally be acwmpanied by erratic side-to-side weave. Again, adjustment of pressure, or replacement of guides and pads, may remedy the trouble, which can be verified with the same test film as noted above. Most projectors are equipped with edgeguiding film slides. These should be checked with a gauge for correct alignment and location. They should be examined for wear, and the tension on the edge of the film should be kept sufficient to prevent weave and lateral motion. Again, the same test loop will measure the results. New or heavily waxed film may cause jumping. This motion is very erratic and can be detected by the noise produced, and possibly by the deposit of wax on the guides. This condition should be temporary and easily isolated by comparing the operation with a normal test loop. Some of the picture jump, or side motion, may be due to inaccurate camera and printer registration during the film processing. This defect cannot be corrected in the projection room, hut it can be isolated by making a comparison with the test loop, which has been carefully processed to minimize such inaccuracies. Shutter Adjustment With the larger pictures more light is needed. In some cases, projector shutter blades have been reduced in angle to a dangerous size. The slightest adjustment change, or least amount of gear back-lash, may produce travel ghost effects. To detect this trouble the SMPTE Travel-Ghost Target test reel should be used. This reel will demonstrate the slightest amount of fringing, or ghost, and its direction. Adjustments or replacement should be made as required. If the shutters are not wide enough, a slight fringe or halo will occur on both sides of the bright sections on the screen and will give the effect of very bad focus. Lenses sometimes are blamed for this effect when actually the shutter and gear train are at fault. Film Curvature and Flutter Wide-angle, high-speed lenses transmit more light, but they are also much more critical in focusing. The permissible “depth of focus” becomes more shallow and the film should be held in one plane to close tolerances. More light means more aperture heat, and tests have indicated that the amount of film curling, or “pin-cushioning,” in the gate varies directly with the heat on the film. Projection Lenses Judging the quality of a lens in a theatre is a very difficult process. This is due to the fact that there are so many other variable factors involved. The physical quality of the film used may be questionable. The amount of film curl may he beyond the depth of field of the lens. The lens mounts or tubes may be vignetting. The light source may not be matched to the lens speed. However, there are some field tests which may help in checking the operating quality oi a lens. The lens holder should be perfectly strong and rigid to eliminate any spurious vibrations. The lens axis should center and be perpendicular to the film picture frame. The lens mount, extension tube, projector front should in no way extend into the light beam. The lamp optical system should be of the same speed as the lens, at least for the rays about the aperture center. To check for lens conditions, use a dummy aperture plate with many small perforations. The images of the perforations should be MIRRORS? uou con. Ao&e fhaWun. uMlfL HEYER-SHULTZ UNBREAKABLE METAL REFLECTORS 5 YEAR GUARANTEE •M/MOmum SCREEN ILLUMINATION SEE YOUR THEATRE SUPPLY DEALER * Manufactured bi( 41EYER'SHULTZ,INC., Cedar Grove, N.J. 28 Motion Picture Herald, March 24, 1956