GB557679A - Improvements in or relating to optical projection apparatus - Google Patents

Abstract

557,679. Optical-projection apparatus. KODAK, Ltd. Dec. 4, 1942, No. 17266. Convention date, Dec. 6, 1941. [Class 97 (i)] In apparatus which is adjustable for varying the magnification of the projected image, the aperture of a light diaphragm associated with the projection lens is varied automatically with the change of magnification so as to maintain substantially the same image brightness. As shown, the diaphragm aperture of the projection lens of apparatus constructed as described in Specification 544,026 is varied simultaneously with adjustment of the lens focus. The apparatus comprises a projector head 3, a fixed projection lens, a movable reflector 9, and a projection screen 5 movable by a pinion 40 and gear segment 39, the reflector and screen being connected so as to move simultaneously to vary the length of throw, and the focus of the lens being simultaneously varied by rotation of a lens focusing sleeve 10 by a cable 28 stretched by a spring 36 and making a round turn between flanges 35 on the sleeve. The sleeve 10 is threaded in a fixed sleeve 13 so as to move axially when it is rotated, and a pin 19 extends from the diaphragm ring 20 into a slot 18 cut in the fixed sleeve 13 ; the restraint on the pin 19 adjusts the diaphragm aperture during the focusing. Hand adjustment of the diaphragm aperture may be effected by rotation of a knob 38 on a shaft 32 eccentrically carrying a circular guide 30 for the cable 28. The pinion 40 may be locked, to hold the members in adjusted positions by means of spring-pressed balls clutching the pinion shaft to a fixed plate ; the balls may be moved to freeing position by pins on extensions 58 of a plate 55 movable by a knob against the action of a spring 59.