GB873286A - Adjustable optical prism system for producing variation in size of images - Google Patents

Abstract

873,286. Optical prism systems. FARLEY. M. P. Aug. 9, 1957, No. 25230/57. Class 97(1) An optical system for enlarging or reducing by an adjustable amount the size of an image formed by rays passing therethrough includes several prism elements which form two interconnected pairs of prisms, each pair forming a unit, the elements and units being so arranged and connected together that at all times the deviation due to one prism of each pair is diametrically opposed to the deviation due to the other prism of that pair, while the deviations of the prisms of one unit are maintained at right-angles to the deviations of the prisms of the other unit. In this system, the pairs of prism elements or of prisms in the individual units are connected together for simultaneous angular movement in opposite directions, the connections being effected by means comprising pulleys, cords encircling the pulleys and movable members to which the cords are attached so that an angular movement of one prism element or prism in one direction is accompanied by an angular movement of the other prism element or prism in the opposite direction. As shown in Fig. 1, two prism units 10, 11 are made up of prisms 12, 14 and 16, 18 rotatably mounted about axes 15, 17 and 19, 29, the refracting edges of the prisms in unit 10 being perpendicular to those in the unit 11. Image-forming rays passing through each prism unit will be deviated in planes perpendicular to the refracting edges of the prisms by an amount depending upon the mutual inclination of their refracting faces. The prisms are preferably of circular form and are housed in a stepped tube 30, one in each section and pulleys 32, 33 and 34, 35 are fixed to each rotation axis. A pulley operating member 36, 54 has attached thereto cords which pass around the pulleys and each operating member is connected to a rotatable sleeve 46 so that, on rotation of sleeve 46 relatively to the stepped tube 30, the pulleys of each pair, and therefore the prisms attached thereto, will be rotated in opposite senses and by equal amounts to provide the required variation in image size. In a second embodiment, each prism is maintained at a fixed inclination to the optical axis and consists of two prism elements which are relatively rotatable in opposite senses to provide the required image size variation.