GB774163A - Luminous output transducer - Google Patents

Abstract

774,163. Modulating light. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. July 18, 1955 [Sept. 10, 1954], No. 20697/55. Class 40 (3). In a light modulator, Fig. 1, in which the image of a triangular aperture 18, Fig. 2, in a mask 16 is displaced with respect to a knife edge 22 by means of a tiltable mirror system 24 actuated by electrical signals applied to electromagnet 24, the varying triangular image transmitted past the edge is projected on to a surface 36 by a beam splitter 30, 32, 34, 38, 40 arranged so that the two images produced are relatively inverted and disposed contiguously to form a square, Fig. 3. A light spot is thus produced which, in response to electrical signals, remains unchanged in shape and position but varies in area. The modulator is employed in making half-term printing plates, surface 36 being a photo-sensitive sheet which is moved relative the light spot whilst the light beam is interrupted so as to build up a pattern formed of discrete spots. The interruption may be effected by modulating the light source 10 electrically, as by generator 43, or by the use of a mechanical chopper or disc located in the light path. It is also possible to interrupt the light by combining suitable pulse signals with the singlas controlling the tiltable mirror. The use of a simple triangular aperture in mask 16 results in the central portion of the spot receiving a greater exposure than the edges due to the finite speed of movement of mirror 24. To compensate for this a mask as shown in Fig. 4, may be employed resulting a light spot as shown in Fig. 5. In a first modification, Fig. 5 (not shown), the beam splitter is formed of a pair of right-angle prisms contacting along a common face provided with a beam-splitting layer. In a second modification, Fig. 7 (not shown), a beam splitter is dispensed with and two separate light sources are provided each associated with its own apertured mask. The tiltable mirror reflects the two light beams to separate oppositely-facing knife edges, the path to one including a reflecting surface so that corresponding displacements of the two beams relative the knife edges take place. Specifications 692,349 and 692,400 are referred to.