GB657047A - Improvements in or relating to cathode-ray tube display systems - Google Patents

Abstract

657,047. Cathode-ray tubes. HANSFORD, R. F., and SPERRY GYROSCOPE CO., Ltd. April 3, 1947, No. 9182. [Class 39 (i)] A display system includes a cathode-ray tube which has an optically clear window 3, Fig. 1, in the bulbous portion of the envelope and close to the electron gun side tube, and the image on the fluorescent display screen 7 produced by the electron beam has superposed thereon a real image of an external field which is projected through window 3 by an optical projection system 4, 6. In one form, Fig. 1, a photographic film or lantern slide 5 is illuminated by source 6 and the image is focused by lens 4 on to the display screen 7. The image on the film may be a map or chart. A condenser lens (not shown) may be interposed between 5 and 6. Lens 4 is non-parallel to film 5 and screen 7 so as to compromise between distortion and sharp definition of the image projected on to screen 7. In a modification, Fig. 2 (not shown), light reflected by a map or chart is subsequently reflected by a mirror and focused on to screen 7. The mirror is so arranged as to minimize distortion of the image projected on to screen 7. The mirror may be replaced by a totally internally reflecting prism. The tube construction may be as in Fig. 3; window 3 is a flat polished glass plate and is sealed to a side tube 2 at 11. The side tube 2 is then sealed to envelope 1 at 12, and finally tube 13 is sealed to envelope 1 at 14. In a modification, Fig. 4 (not shown), the tube 13 is sealed to envelope 1, side tube 2 is then sealed to envelope 1, and finally a thimbleshaped window of thin glass is sealed to side tube 2. In the latter case lens 4, Fig. 1, may be located within the thimble. Instead of the window 3 being sealed to a side tube 2 it may be sealed direct to envelope 1. The window 3 may form part of the focusing lens. The Provisional Specification states that optical compensating means may be disposed in the optical path to correct distortion of the projected image due to the axis of projection not being normal to the display screen and refers in addition to a form using a semitransparent mirror, so that images of both a film and a map may be simultaneously projected on the viewing screen of the cathode-ray tube.