Motion Picture Herald (1953)

Zk J^eedlZs Sye A Department on PHDJECTIDIV & SDUIVD "2Vo other art or industry in the world narrows down its success to quite such a NEEDLE’S EYE as that through which the motion picture has to pass — an optical aperture — in the continuous miracle of the screen by a man and his machine, the projectionist and his projector.” — TERRY RAMSAYE. How Faulty Sprocket Teeth Injure Film— Threaten Fire! Detailing causes of film damage which, while not of a kind to injure the screen image, is otherwise a projection hazard and a fire hazard as well — fourth of a series of articles on accessories and film handling. BY CIO GACLIARDI THE CAUSES of film damage that becomes hideous blemishes of the projected picture, were observed in this department of the January issue of Better Theatres. Serious film mutilation can be produced also by badly worn or damaged projector and soundhead sprockets. This type of damage runs a close second to film scratching. Although it may not be visible to the audience, sprocket hole damage may produce even worse effects — film jamming and film fire. During projection, sprockets may produce damage to film due to one of the following causes : (1) Badly worn sprocket teeth; (2) damaged sprocket teeth; (3) poor alignment between sprockets, film, shoes and guide rollers; (4) excessive tension by upper magazine brake, on film gate shoes, and from take-up clutch; (5) shrunken or deformed film. Motion picture film is propelled through the mechanism by means of toothed sprockets and acts just like the roller chain and sprocket drive in an ordinary bicycle. The bicycle chain however is made of steel and is lubricated, whereas the film is made of thin, flexible plastic and is also bone dry. The teeth in a projector sprocket are supposed to register exactly in the film sprocket holes so that the film is engaged and pushed at the base of the tooth, not by the narrower tip or intermediate section of the sprocket tooth. In a properly fitting sprocket, the tips of the entering and leaving teeth should never touch the film, otherwise chattering and jumping will surely occur. It is obvious that where a greater number of sprocket teeth are in contact with the film at the same time, less wear may occur since each tooth does less work. For this reason some manufacturers have increased the diameter and number of teeth on their upper and lower sprockets, thus producing greater contact surfaces and reducing wear at these points. Intermittent sprockets, however, have remained pretty much the same; and here is a point where most extreme care must be observed to prevent film damage. INTERMITTENT ACTION At all other sprockets the film is in constant motion at a speed of 90 feet per minute, but at the intermittent sprocket the film starts from a stationary position and moves one whole frame in 1/96-second. It then remains stationary for 3/96-second and then moves one whole frame, etc. {See Figure 1 ). This means that the film during its motion across the projector film gate must reach a peak velocity of 860 feet per THE TREND IS TO STARCORED For quality and quantity — the light produced with Lorraine Carbons is unsurpassed. The Star-Core feature of the positive Lorraine Carbons is your guarantee for a brighter, whiter and steadier light— more evenly distributed over the entire surface of the screen . . . more economically! CARBONS, INC. BOONTON, N. J. BETTER THEATRES SECTION 45