Filmo Topics (Jan-Dec 1931)

FILMO TOPICS Film Control in the Channel Article No. 13 of the "Facts About Filmo" Series, explaining how film is accurately registered at the Filmo Projector's Aperture JOSEPH A. DUBRAY Figure 1 Showing the film movement mechanism of the Filmo 57 Projector. A — aperture; C — shuttle tooth at middle of down stroke; G — guide rail; T — tension spring J.N concluding the preceding article of this series we pointed out the necessity, in a projector, of protecting the film surface from the marring which friction would cause. To be fully successful in every respect, the mechanism of the projector's film channel must be designed not only to provide extremely accurate film registration at the aperture but freedom from film-damaging friction as well. How these requirements are met in the Filmo Projector will be told in this article. In considering the matter of placing each successive frame of film accurately at the aperture, it must be rembered that this precise positioning must be maintained in not one or two but three planes — vertical, lateral, and longitudinal. Lack of accuracy in vertical registration would result in jerky, unsteady screen pictures and even in visible frame lines — the bottom of one picture showing above the top of another. Failure to achieve perfect lateral registration would be evidenced by sidewise movement on the screen, while inaccurate longitudinal registration would produce out-of-focus pictures. The film channel mechanism of the Filmo Projector provides for precise registration in all three planes, doing this in a most ingenious way — in a way which results in kindly treatment of the film. The only pressure exerted on the film is applied along the side, rather than on the flat surface. At one side of the aperture the film edge rests against the stationary guide rails G, Figure 1. On the other side of the aperture the tension springs T exert a carefully calculated pressure which holds the film against the guide rails. Thus lateral registration is secured and thus the film is held stationary before the aperture A while the shuttle tooth C is withdrawn for its return trip to engage with the next perforation. Vertical registration is, of course, aided by the efficiency of the guide rails and tension springs in overcoming momentum, but is primarily controlled by the shuttle tooth. The work of this tooth is very light, since the commonly employed method of exerting heavy back pressure upon the film surface is not used in the Filmo Projector. Therefore the shuttle tooth has merely to guide the film on its path through the channel. The action of this tooth was fully described in Filmo Topics for November. It engages the perforation with a straight forward (not a clawing) movement, and is of such size that it practically fills the perforation. Before it has acquired its full downward speed it begins to move the film. Therefore there is no sudden striking of the perforation edge which would tend to cause wear on the film. The placing of the shuttle tooth right beside the aperture and the accurate mechanical control of its motion (see No Figure 2 (Lefl) Back plate of the film channel. B-Rollcrs. R-Spring Rails Figure 3 (Right) Lens Carrier. B-Rollers. DLever. E-Clearance adjusting eccentric vember Filmo Topics article) result in perfect vertical registration. Longitudinal registration must also be precisely accomplished. That is, the film must be maintained in an exact position with regard to the focal plane of the projection lens. Any frontward or backward motion would result in a screen image lacking in sharpness, or "breathing" in and out of focus. This registration is secured by spring actioned rails (R, Figure 2) which are a part of the projection lens carrier. Before threading the projector, the lever D, Figure 3, is raised to bring the lens carrier forward. This permits inserting the film in its channel. Then the lever is brought down again to reset the lens carrier in operating position. This automatically brings the rails to such a distance from the aperture plate that they permit free passage of the film, with sufficient clearance to eliminate friction. Still the clearance is scant enough to prevent the film from running in a plane outside the permissable tolerances of the projection lens. The only possible contact with the film surface is on its margins. One of the two spring rails, as may be seen in Figure 2, is slotted to permit the passage of the shuttle tooth. The spring action of both is calculated to permit the double thickness of film found at splices to pass through the channel without effort. The projector's clearance is adjustable by means of an easily accessible screw (not