The motion picture projectionist (Nov 1931-Jan 1933)

March, 1932 Motion Picture Projectionist 17 A Portable Non-Intermittent Projector * t A portable projector made by the Etablissement Gaumont Franco-Film Aubert is described. The projector is of very small weight and is arranged for carrying in a case. The fibm moves with a constant motion past the axis of the light source and the projection lens, the image being maintained stationary upon the screen by a combination of the movement with an optical "compensator." It is claimed that due to these features wearing of the film has been very much reduced and the motion is extremely silent in operation. The article describes briefly the optical principle of the motion, how the principle is applied, and the construction and assembly of the apparatus. THE "Simplicine" is a cine projector for standard film, selfcontained and complete, yet small enough in bulk and weight to be portable. The whole projector is enclosed in a metal casing and can be carried easily on a sling strap. Its erection is almost instantaneous and its manipulation so simple that no special experience is required for its use. The chief importance of this machine, particularly so far as the nonprofessional user is concerned, is that it employs the principle of constant movement projection. The film moves with a uniform motion across the axis of the light source and the projection lens. This is a vital difference from the usual intermittent projector, in which a Maltese cross or other mechanism is used to drag the film into position and then bring it momentarily to a standstill in the gate of the machine. In the new projector the image is kept stationary on the screen by means of a special combination of the B 1 °'t 1 O t c 3 Fig. 1. Illustrating the Optical Principle movement with an optical device termed a "compensator." One greater advantage of such a system is the very much reduced wear on the film perforations owing to the elimination of the violent and repeated tugs to which films are subjected in ordinary types of projectors. Film is said to last five times as long when it is run in this continuous manner. To this advantage may be added the not less important one that absolutely silent * Translated from Revue d'Optique. t Courtesy of the S. M. P. E. Journal. mechanism can be obtained when all the moving parts are given nothing but continuous rotary movement, as is the case in the "Simplicine." The Optical Principle Fig. 1 represents a film moving in a downward direction and carrying a series of images 1, 2, 3, etc. Imagine that in front of these images is a series of similar lenses Oi, 0=, 0^, etc., each having its focal point in the plane of one of the images, and suppose this chain of lenses to move in a direction parallel with the film and at the same speed. If the beams of parallel light so formed meet a fixed lens C the images of the different elements of the film will be superimposed in the focal plane of this lens. Indeed, if we consider an element formed by an image on the film and the corresponding lens, the image of a point of this element given by C will have its position, in the focal plane of C, determined solely by a straight line passing through the optical center of C and parallel to the straight line joining the given point in the element to the optical center of the corresponding lens. Now this straight line as it moves remains parallel, consequently the final image is fixed. This is true for all images of the points of the element of the film. The straight lines joining corresponding points of the element to the optical centers of the corresponding lens being parallel, the images of successive elements are superimposed in the focal plane of C. Hence the projection screen E is made to take the position of the focal plane of C and focusing for various distances is obtained by providing a set of lenses C of different focal lengths. How the Principle Is Applied The realization of this principle in actual fact has been achieved in the following manner: The lenses are set round the periphery of a cylindrical drum T (Fig. 2), which is free to turn on its axis. T is made to rotate by the fact that the film catches a tooth D formed on the drum and carries T round with its own movement. The lenses therefore move at the same speed as the film. Light passing through the illuminated film reaches the lenses O after traversing a prism P (Fig. 2), which is formed integrally with the fixed axis of the drum. This prism has two reflecting surfaces Mi and Mz set perpendicular to one another. The system thus produced is that indicated in Fig. 1, with the difference that the film and the lenses do not travel in a straight path but fol Fig. 2. Construction of Lens Drum low curves of the same radius. This difference has a practically negligible effect on the quality of the images, assuming that the film is illuminated only1 over the length of two images. This means that two images and two only of the chain of lenses are actually utilized, film elements and lenses which have any appreciable inclination to the normal being kept out of action. Furthermore, the projected image shows its maximum illumination at the moment at which the corresponding lens has its axis coincident with the axis of projection, and the effect of this is to reduce greatly the aberrations of the images thrown by adjacent lenses which are slightly inclined. This mechanism is exceedingly simple: it consists of a single component moving with a continuous rotary movement at low speed — 80 revolutions a minute for a projection speed of 16 pictures a second. Wear is therefore reduced to a minimum and the running is quite noiseless. The Projector Described The "Simplicine" has been given the form of a rectangular case, the top and side of which are formed with hinged swinging sections which are raised vertically for use. All the mechanism is then made visible. The feed-reel, 3 (Fig. 3 and 4), with its pulley, U, is then fixed on this raised portion of the casing. The film passes under the feed sprockets, 5, and on to the drum T carrying the compensating lenses; then on to the toothed sprocket 6, the take-up reel 7, rotated by its drving pulley 8. Masking the film on the screen is effected thus: when the lever, 9, is pressed downward, the roller, 10, is pushed up between the two pressure rollers, thus raising the film and rais