GB700573A - A device for verifying optically projected images - Google Patents

Abstract

700,573. Kinematograph &c projection apparatus. ANGENIEUX, P. July 23, 1951 [Oct. 5, 1950], No. 17388/51. Class 97(1) A device for verifying optically projected images comprises a first reflector in front of the projection lens, inclined to its axis, to reflect a small part of the projection beam on to a second reflector, approximately normally, the latter reflector constituting or coacting with a centred optical system to form a sharp secondary image on an auxiliary screen in the projection booth. The first reflector may be partially reflecting or may cover only part of the cross-section of the projection beam. As shown, an unsilvered glass plate 17, with a low reflection coating on the face 18, reflects light from the projection lens 14 to a concave mirror 20 and thence to a plane mirror 21 to form an image on the translucent screen 22 which is correctly oriented when viewed through the screen. The mirror 20 may be replaced by a plane mirror and a positive lens. Further mirrors may be used to obtain a longer folded light path and a larger secondary image To maintain correct image orientation two such mirrors are required between the plate 17 and the screen, but only one between the plate and the mirror 20. A negative lens, or lens system, may be used between the plate and screen to increase the image size. A cone-shaped member 23 connects the housing 16 with the aperture in the wall 24 of the projection booth. The plate 17 and the screen 22 are sealed into the housing to isolate the booth for fire protection purposes.