Motion Picture Herald (1953)

PfcjecthH 1. Picture Streaks SOME AMOUNT of damage may be suffered by film in exchanges and in transit from theatre to theatre ; however, most film damage occurs in the projection room, and specificall\' in the projectors. MAGAZINE VALVE ROLLERS Probably more prints are discarded because of severe and multiple scratching than for any other reason, and the most prolific sources of this type of damage are the maijazine valve rollers. Because these rollers are grouped so closely together, with some of them arranged to float on the film, they form a close nest or trap which can gather dirt, oily matter and film chips, d'his debris may slow down the rollers or may even stop them completely. When this happens, the raised-end tracks of the rollers will wear down sufHcienth' to permit the central part of the roller to have direct contact with the him. This particular type of trouble is more prevalent on the upper magazine valves because the concave section of the magazine funnels everything into the valve assembly. Even when the rollers are kept clean and free, some cases have been found where the white-metal casing, which normally comprises the bearing surface for the roller bearing pins, has worn sufficiently to allow the hotly of the rollers to rub against the trap frame. I'his extra friction will also stop the rollers with the same disastrous result to the film. Concerning this kind of film scratching the Eastman Kodak Company reports that the relatively soft emulsion of new prints is very susceptible to abrasion, and the scraping is frequently so deep that the emulsion is completely plowed off. Since these rollers are on both sides of the film, nonemulsion side scratches show up as dark lines on the screen, especially when they become filled with oil and dirt. COLORED DUPLITIZED FILM With certain types of colored duplitized film, tliere are two emulsion sides which are affected. Damage here will result in red and green “rain” or deeper lines. Clogged and Film Damage and Its Prevention damaged rollers may produce long straight scratches, or a repeating pattern of short scratches as the rollers jerk in their motion, or as the film weaves from side to side. The only remedy for this kind of trouble is repeated inspection of the magazine trap rollers and bearings, both front and back. Ehe screw pins on the rollers are generally hardened and ground and a few drops of oil will prevent rusting and eliminate friction. The film, while in motion, pulls these rollers around, and excessive friction causes the roller faces to slip on the film. Some rollers come through with a black oxidized finish which helps in detecting defective roller operation, because when film rubs on the hlack central section of the roller, it polishes, or removes, the coating, thus giving a warning of impending trouble. d'here are certain types of roller housings which have been carefully machined and wdiich have special bearings installed for the roller pins. These will give longer operating life with less possibility of scratching trouble. UPPER MAGAZINES I’pper magazines should be free from all encumbrances and should be easily removable so that the upper rollers may be better inspected and thoroughly cleaned. Some magazines have incorporated in the frame of the rear window a low-voltage lamp which serves to give warning about the level of the film on the reel hub. Some magazines are equipped with very effective constant-torque retard clutches which provide a continual, smooth retarding pull on the reel spindle. Such a device is invaluable in preventing film overfeed through sudden retard and snapping. If an audible warning must be used, it is definitely safer to use one whose whole mechanism is completely outside the magazine and has no contact with the film. GUIDE ROLLERS After the film leaves the upper magazine, it is fed by the upper sprocket into the film gate or trap. The film here must be guided perfectly, held in rock-steady position during projection, and then moved into a new position. The guide rollers above the gate serve as a guide for the film as it travels down past the aperture to the intermittent sprocket. On older projectors these rollers are the only form of edge guide for the film, but on newer models the long film tracks on the side of the aperture have been recessed to provide full-length film guiding and edge support. It is imperative that the rollers and runners be aligned properly with the intermittent sprocket, otherwise the teeth will engage the film perforations off-center, and the corners of the perforations will be broken. The guide rollers must run freely or they may develop grooves and ridges which may further damage the film edges and even open up poorly made splices. 1 he guide roller assembly should be inspected frequently and if necessary removed for cleaning or replacement. The guide roller tension springs should be checked to see that they still have proper tension. GATE TENSION The principal reasons for using pressure pads and shoes on a film trap is to prevent picture jump and to maintain a basic focusing plane for the film. Insufficient pressure by the pads will permit the film to stop at different positions causing picture jump. Excessive pressure will result in abnormal Him wear and damage. There seems to be no generally accepted standard setting of pad pressure for any given projector which is satisfactory to all projectionists. The Eastman research labs have made tests on various projectors over a long period of time and have concluded that a total equal pad pressure which demands a film pull of over 16 ounces is unnecessary and only increases wear on the Him; while settings producing pulls as loiv as 6 ounces appear in some cases to be sufficient to give steady screen pictures. 2. Sprocket Damage Serious Him mutilation can be produced also by badly worn or damaged projector and soundhead sprockets. This type of 20 Motion Picture Herald, March 21, 1953