Patent GB-976579-A (GB)
Title: Wide angle projection system
IPC: G03B37/00
Filed: 1962-04-03
Abstract: 976, 579. Optical projection systems. COLORVISION Inc. April 3, 1962 [April 10, 1961], No. 12696/62. Heading G2J. A wide angle projection system for simultaneously projecting a plurality of images with a single light source upon a screen includes projection lenses, means at the light source for directing substantially all of the light emanating therefrom along two or more light paths, said light directing means including condenser lenses for each light path and means in each light path to relay an image of the light source provided by the condenser lens to the respective projection lens and to also image the respective condenser lenses at a film plane, each said relay means including a relay lens located at the aerial image of the light source provided by the condenser lenses. In the embodiment shown, light from a single light source in a projector 10 (Fig. 1) is divided by beam splitting mirrors and dichroic mirrors into five beams, two of white light for projecting a map image M and a white overlay W on to a screen S and three of red, green and blue light respectively for projecting additional information in superposition on to the same screen (image R, G and B respectively). In each light path between a condenser lens C (Fig. 5) and a projection lens P there is provided a relay lens R located at the aerial image of the lamp L formed by the condenser lens, and an aperture lens A adjacent a film plane F. The relay lens serves to image the condenser lens at F whereas the aperture lens images said aerial image at a nodal point of the projection lens P. Two condenser lenses 24 and 25 (Fig. 4) are provided at the lamp 11, in co-operation with a spherical reflector 30, and two dichroic mirrors 33, 34 in main light beams 28, 29 serve to transmit I.R. radiation out of the system to avoid overheating at the film plane F. White light reflected from the mirror 33 is further divided into two portions by a semi-transparent mirror 38, the transmitted portion 37 being directed to a projection lens 12 (for the map image M) by way of a mirror 39a, a relay lens 39, mirrors 40, 42a, b and c and an aperture lens A. The reflected portion 36 from the mirror 38 is directed to a projection lens 13 (for the white overlay image W) by way of a mirror 44, a relay lens 45, mirrors 46 and 47 and an aperture lens 19. White light reflected from the mirror 34 is divided into red, green and blue beams respectively by reflection successively at dichroic mirrors 50, 59 and 72, an ordinary mirror 71 being interposed in the light path between the latter two. Remaining I.R. and other unwanted radiation is transmitted out of the system. Red light reflected from mirror 50 is directed to projection lens 16 by way of mirrors 52a and b, a relay lens 53, mirrors 54-57 and an aperture lens 22. Green light reflected from mirror 59 is directed to projection lens 15 by way of mirrors 61a and b, a relay lens 62, mirrors 63-66 and an aperture lens 21. Blue light reflected from mirror 72 is directed to projection lens 14 by way of a mirror 73, a relay lens 74, mirrors 75a and b, 76 and 77 and an aperture lens 20. Adjustable diaphragms may be provided for each projection lens. In a modification, three condenser lenses may be provided around the lamp 11, each receiving light through 120 degrees arc. In this case no rear reflector would be necessary. Two different images may be separately projected onto separate adjoining areas of the screen. The film may be retained in the film plane by a stream of air which also serves for cooling the film.