Patent GB-632817-A (GB)
Title: Improvements in and relating to kinematographic projection with continuously moving film
IPC: G03B41/08
Filed: 1947-05-02
Abstract: 632,817. Kinematograph continuous-feed projectors. SCOPHONY, Ltd., and COOK, G. H. May 2, 1947, No. 11929. Addition to 589,971. [Class 97 (i)] In a kinematograph projector of the kind set forth in the parent Specification, the compensating means comprises means for changing the position occupied by the projection lens operative during successive flashes in each frame period or, when the number n of flashes per frame period is small, the compensating means comprise n fixed lenses and means for rendering these lenses operative in succession during successive flashes in each frame period or the compensating means comprise several reflectors arranged to be brought successively into the light path between the film and the projection screen and at the same time to vary the length of the light path and means for displacing the projection lens along its optical axis in step with the changing of the operative reflector in order to compensate for the variations in path length. As shown in Fig. 1, a number of like lenses 10 equal to, or an integral multiple of the number of flashes per frame period is mounted in apertures in a disc 11 which rotates about an axis 12 orthogonal to the plane of the film and passing through the centre line thereof. The disc revolves once per frame period and the film is illuminated whenever a lens is in register therewith. Movement of the film between successive flashes is compensated by arranging the adjacent lenses so that the distances from their respective centres to the axis 12 differ by Mp/n (M+ 1), where M is the magnification produced by a lens, p is the film pitch and n is the number of flashes per frame period. The film may be arranged to one side of the axis 12 so that the tangent to the direction of motion of the operative lens is parallel to the direction. of the film movement; in this case, the lenses on the disc are arranged so that the distances between adjacent nodal points differ by the amount defined above, while the distances between the adjacent nodal points and the axis 12 may be constant or, preferably, may vary. In another form, the arrangement is such that one lens is operative for the whole of one frame period, the lens adjacent thereto being used as a compensator during the next frame period and so on; the lenses in this form are mounted either on a disc of large radius or on a drum, the axis of which is orthogonal to the lens axes. Also, a single lens may oscillate rectilinearly as by means of a cam to bring it into the required position at the times of the successive flashes. When the number of flashes is small, two for example, lenses 17 and 18, Fig. 5, may be positioned with their optical axes parallel and separated by the defined distance, segments being cut out of the lenses when this distance is less than the diameter of one lens; a shutter 19 renders these lenses operative in turn during successive flashes. A lens may also replace the glass block used in the arrangement described in Specification 629,179, wherein two mirrors revolve about a single axis, the lens being movable so as to be separated by equal amounts from each operative mirror.