American cinematographer (Jan-Dec 1928)

January, 1927 AMERICAN CINEM ATO GRAPHER Nineteen Lubrication of M. P. Film (Continued from Page 9) duce an incrustation on the gate than "green" film and this is usually attributed to the burnishing or polishing action of the aperture plate or pressure springs on the gelatin coating of the film. The burnishing effect produced by projecting the film in a Simplex projector, ten times is very slight as shown in Fig. 7 (magnification 540). This is a photomicrograph of the film surface in the region between the perforations. The lower half of the figure shows a portion of the film surface which was in contact with the aperture plate. The burnishing effect on the film surface is negligible. It is considered that traces of oil which are transferred to the film surface during the first projection are chiefly responsible for the increased ease of passage of the film on subsequent projection. It is obvious also that the moisture content and degree of hardening of the gelatin coating are important factors which determine the rate of formation of the incrustation in the gate. If the gelatin coating of the film contains an excess of moisture, it tends to soften and become "tacky" much more readily in the hot projector gate than is the case with dry film. This tendency of the gelatin coating to soften under the action of heat can be diminished by hardening during processing. 'However, excessive hardening tends to increase the brittleness of the film and is not to be recommended. 2. Apart from the condition of the film, the following factors relating to the conditions existing in the projector also determine the extent of the formation of the gate incrustation. (A) The tension of the gate springs. This should be of the order of eight ounces for each spring or a total of sixteen ounces. The spring tensions should be adjusted individually at intervals by attaching a spring balance to the upper end of a narrow film strip placed at one side of the gate and increasing or decreasing the gate tension until the film just commences to travel upwards when the spring balance registers eight ounces with an upward pull. In a like manner the tension with full width film should be adjusted to sixteen ounces. (B) The nature and smoothness of the gate surfaces. The nature of the gate material in contact with the film surface, providing it is of sufficient hardness, is of less importance than its degree of smoothness. Satisfactory materials are cast iron or stainless steel, either plain or chromium plated. Corrosion should be carefully guarded against and any gelatin incrustation removed with a wood or bone scraper so as not to scratch the polished surface. (C) The temperature existing at the gate. As explained above, the tendency of the gelatin to incrust on the gate springs in the case of freshly processed film increases with temperature. Any means of reducing gate temperature such as the use of heat absorbing glass, a blast of air impinging on the gate, or suitable radiating fins on the gate, is desirable. Methods of Facilitating the Passage of Motion Picture Film through the Projector Even though a projector is in good mechanical condition and the above requirements are fulfilled, there is invariably a tendency for a gate incrustation to form with "green" film. Numerous methods of treating the film to effect this have been suggested from time to time as follows: 1. By Edge Burnishing the Gelatin Surface. It was considered that if the burnishing effect of the gate springs on the gelatin coating of the film could be simulated by a preliminary treatment, the difficulty caused by incrustation might be diminished. Accordingly, a machine was constructed for burnishing the edges of the film (see Fig. 8) consisting of a highly polished undercut roller (Rl) working against the edges of the film and revolving in contact with and above an idler roller (R2). The film was fed between rollers Rl and R2 by means of a gearing so arranged that the film advanced American Cinematographer and Photo-Era if taken separately, cost $5.50 per year. By taking advantage of a special clubbing offer arranged between these two journals, both may be had, on a year's domestic subscription, for $4.15 A. reached offices— S. C. members are seldom available ; when they are, they may be through the A. S. C. -GRanite 4274. HARRY D. BROWN Cinema Studios Supply Corporation 1438 Beach wood Drive HOlIy 0513 HOlly 0514 BrownAshcraft Carbons and Other Studio Lamps Studio Equipment FOR RENT 1 Mitchell Friction Tilthead and Tripod 3 Mitchell Cameras 2 Bell & Howell Cameras Equipped with Astro Lenses. F 1.8, F 2.3 8 Mitchell Magazines Extra Lenses Baby Tripods J. R. LOCKWOOD Hollywood Address Producers Film Laboratories, 861 Seward. GL. 6115 523 N. Orange St., Glendale. Glend. 3361-W JOE NOVAK, A. S. C. Free Lance Akeley Specialist Phone: WH. 3920