GB549645A - Improvements in or relating to duplex optical projection apparatus - Google Patents

Abstract

549,645. Optical-projection apparatus. KODAK, Ltd. May 27, 1941, No. 6788. 'Convention date, July 25, 1940. [Class 97 (i)] Change-over shutters for two projection apparatus are operatively connected with driving means causing one shutter to open and the other to close with simple harmonic motion, so that the screen brightness is substantially constant during the change-over. As shown, the members of each of two pairs of shutter blades 31, 33, and 48, 56 respectively, move laterally towards one another to meet centrally in one beam while those in the other'beam move apart, an'd vice versa. 'The blades 31, 33 are respectively carried by parallel bars 24, 27 pivoted to_parallel arms 16, 17 centrally carried on pivots 18, 19. A spring 42 connects the arms 16, 17, to maintain engagement between an L-shaped member 38, pivoted thereon, and one or both of two rollers 69, 70, mounted near opposite ends of a diameter on a rotatably driven disc 68. Similar members are provided in connection with the blades 48, 56 to maintain an L-shaped member 60 in engagement with one or both of rollers 71, 72 mounted near opposite ends of a diameter on the other side of the disc 68. The two diameters are at right angles to one another, with the result that the phase difference of the harmonic motions of the blades in the two beams is 90 degrees and the illumination of the screen during the changeover is substantially constant.