GB397418A - Improvements in or relating to the mounting of objectives for use with cinematograph and like projectors - Google Patents

Abstract

397,418. Optical-projection apparatus. SOC. POUR L'EXPLOITATION DES BREVETS A. G. 1., 88, Rue des Dames, Paris. March 29, 1933, Nos. 9525 and 9526. Convention dates, April 9, 1932, and Oct. 21, 1932. [Class 97 (i).] In an objective mounting for a kinematagraph &c. projector, means are provided for varying the focal length of the objective to alter the size of the image, and simultaneousl y varying the inclination of the objective axis to the horizontal to such an extent that the lower edge of the image area remains at a fixed height on the screen. In the form shown, the objective 1, the focal length o f which can be varied by rotating the forward lens ring 1a, is mounted within a cylindrical casing 2 on which is rotatably mounted a ring 7 having a projection 8 engaging a pin 9 on the ring 1a. At its rear end the casing 2 is formed with bearing surfaces 10 engaged by screws 11, Fig. 7, carried by the support 12 secured to the projector. The member 12 has forwardly extending arms 13 between which is mounted a shaft 14 to which is secured a cam 15 and an arm 16. The cam engages a cage 20 having upwardly extending arms 21 carrying trunnions 22 engaging in the casing 2. A cable 17 connected at one end to the arm 16 passes round a groove 24 on the ring 7 and is secured at its other end to the ring. When the shaft 14 is rotated by the handle 18 the cable turns the ring 7 to alter the focal length of the objective and therefore the size of the projected image, and at the same time the cam 15 acting on the cage 20 causes the casing 2 to turn on the pivots 11 to maintain the lower edge of the image in a fixed position. A spring within the ring 7 effects the reverse rotation of the ring when the handle 18 is turned in the opposite direction. The objective 1 can be adjusted axially in the casing 2 to focus the image by means of an eccentric pin 3 engaging in the objective and rotatable by a head 3a. The pin is mounted in a carriage 4 which can be displaced axially along the casing by means of a nut 6. In a modification the objective is mounted in a carriage having a curved face which can slide over the correspondingly curved face of a fixed guide plate, these two parts being provided respectively with a pinion and a rack, and the pinion being connected by gearing to the rotatable ring which varies the focal length of the objective.