International projectionist (Jan-Dec 1950)

The 35-mm Projection Positive Film By ROBERT A. MITCHELL V. The Film Print and Its Handling PHYSICAL injury to projection prints may occur in the processing laboratory, in the film exchange, in transit to and from theaters, and in the projection room. The photographic faults which arise through poor camera work and processing must be distinguished from physical damage, but such faults are nevertheless of great importance to the projectionist. "What projectionist has not at one time or another received complaints of poor light when running a print so dense that no amount of illumination would provide the screen image with satisfactory contrast values? Likewise, 'development flicker' may be charged to an unstable arc; incorrect 'gamma' (contrast factor) to a soiled lens; poor camera focus or print 'fuzziness' to poor projector focus; and print unsteadiness to troubles in the projector mechanism."1 A vast amount of damage is caused by improper or insufficient waxing of new prints by the film laboratories. Projectionists sometimes overcome this defect by "oiling" new prints; but it is only fair to say that perfectly satisfactory methods of lubricating films have not, as yet, been devised. 'Green' Emulsion Deposits The emulsion of new ("green") prints is soft and easily affected by heat, which tends to melt the gelatine and make the emulsion gummy and sticky. The coating of the perforation margins on the emulsion side of the prints with carnauba wax minimizes, but does not prevent, the "sticking" of new prints during the first few projections in machines using highpowered arclamps. The sprocket holes of the film may be irreparably damaged. Sticking is evidenced by a violent chattering of the film in the projector and by an extremely jumpy screen image. It is always necessary to remove hardened emulsion deposits from the projector gate after each reel of green film is run. The lubrication of new prints by applying oil to the sides of the film roll, while not approved by either film manufacturers or exchange officials, is certainly much better than smearing the projector gate with vaseline or squirting 1 "Projection-Room Handling: of Prints," by Robert A. Mitchell; IP for March 1948, p. 5. oil on the film as it runs through the projector. Most film damage arises through hasty inspection and careless repair of prints in the exchanges. The film examiners are seldom allowed time enough to patch the prints, or even to inspect them thoroughly, hence the task is passed on to the projectionists. The high-speed winding of film on rewinders in worn condition, not correctly aligned, or without sufficient hold-back tension on the dummy element, scratches the film, weakens splices, and roughens and nicks the edges, particularly when bent reels are used. Such mistreatment may be inflicted on the film both in exchanges and in theaters. The bad practice of "pulling down" loosely wound rolls of film in order to tighten them causes "rain" by scratching both sides of the film. An enormous amount of print injury comes about during shipping, particularly when the film is wound on bent reels and packed loosely in damaged shipping cases. "Shipping damage" is evidenced by bent and torn edges which require trimming with scissors, or even complete removal of the damaged footage. Damage During Projection Film damage may occur during projection by (1) too great a film-gate tension, causing torn and cracked perforations (2) worn sprocket teeth, which also tear perforations (3) worn and incor FIG. 1. Examples of damaged film perforations. A indicates normal wear, excessive gate tension, and worn sprocket teeth. B indicates excessive takeup tension and worn hold-back sprocket teeth. C indicates excessive gate tension (especially on new prints) and hooked intermittent sprocket teeth. D and E are common defects, but the cause is obscure. F and G are familiar examples of torn sprocket holes due to rough handling and improper rewinding. rectly adjusted sprocket idlers, causing the edges of the film to shear and the film to jump off a sprocket and become indented by the sprocket teeth (4) worn rollers and accumulations of dirt in the fire valves, causing soiled and scratched film, and (5) the unavoidable heat of the gate and intense concentration of radiant energy impinging upon the film at the aperture. 1. Gate Tension. This should be uniform and exert a "drag" on the film between 8 and 24 ounces, the exact value depending on the make of projector. A gate tension of about 12 ounces is average. A tension in excess of 24 ounces is definitely not recommended. 2. Sprocket Teeth. Worn or hooked sprocket teeth are especially damaging to film perforations. Worn sprockets should be reversed or replaced. In most projectors, the intermittent and soundhead hold-back sprockets wear the most rapidly. 3. Sprocket Idlers. An idler roller should be separated from the face of the sprocket by a distance equal to 2 thicknesses of film. All idlers must be aligned so as not to shear the edges of the film. 4. Fire Valves. The fire-valve jj>ox should be kept scrupulously clean tti avoid scratching the film. Dirt, in the 4roller type of fire-valve may cause the film to jam and tear at splices: Worn and scored rollers should be replaced. 5. Gate Heat. By far the greater amount of heat absorbed by film' in passing through a projector comes frorti the hot metal runners which contact the perforation, margins of the film. Some heat is also radiated from the metal of the gate to the picture portion of the film, but very little of the intense heat of the light beam to which the filmpictures are exposed, frame by frame, is retained by the film. This may seem strange when we stop to consider that the temperature of the gate runners is 30° C. to 100° G. (86° F. to 212° F.) while that of a lampblack-coated piece of metal held in the light beam at the aperture ranges from 300° C. to more than 1,000° C. (572° F. to more than 1,832° F.), but it is true in almost every case and is easily demonstrated. Determining Heat Level The bulbs of suitable thermometers may be held against the film just below the intermittent sprocket. When allowances are made for the conduction of INTERNATIONAL PROJECTIONIST MARCH 1950 15