Patent GB-573008-A (GB)
Title: Improvements in television
IPC: H04N3/34
Filed: 1943-08-26
Abstract: 573,008. Television; photo-electric range finding. BAIRD, J. L. Aug. 26, 1943, Nos. 13887/43, 15851/43, 16413/43, 16581/43, 19825/43 and 2370/44. [Class 40 (iii)] A television apparatus comprises a photoelectric range-finding device, whereby a signalling current is produced related continuously to the distant or range of the point of the object being viewed by the transmitting apparatus. This signal may be used to control the focussing of the scanning apparatus, or may be sent to a receiving apparatus to produce an image in three dimensions. A range-finding device comprises two photo-electric cells A, B, Fig. 1, one behind the other, adapted to receive light from spots E<1>, E<2> scanned through a lens D by a cathode-ray tube C. The differential illumination of the cells is a measure of the distance of the spots. The electric outputs of the cells are supplied to a valve circuit M which yields a current proportional to the distance of the spots. Another range-finding device oomprises a lens 51, Fig. 3, for focussing light from a cathode-ray tube 50 on an object 52, and a lens 53 near the lens 51 for directing the light reflected from the object on to a revolving mirror drum 54 which reflects the light on to a set of parallel linear photo-electric cells 55. This construction is somewhat similar to the arrangement described in Specification 373,196. The particular cell receiving the light depends on the angle between the incident and reflected light beam, which angle depends at any instant on the distance of the illuminated spot of the object. In another rangefinding device, the range is measured by a differential focussing effect ; and in still another device, the range is measured by a differential frequency produced by means of a. light grid. For controlling the focussing of the scanning apparatus according to the range of the spot illuminated, the arrangement of Fig. 2 may be used. The spots or objects 8, 9 are scanned by light projected from a cathode-ray tube 4 by lenses 5, 7 and a cam-shaped mirror 6 ; and the position of the cam-shaped mirror is automatically adjusted by the photo-electric range-finding device 1, 2. For reproducing images in three dimensions, the arrangement of Fig. 1 may be used. The screen of a cathode-ray tube F is viewed by an eye K through a cam-shaped mirror H and a lens G. Line scanning is performed by the cathode-ray tube and frame scanning by the mirror. The cathode-ray is modulated in intensity as usual, and in addition is deflected out of the straight line in accordance with the range of each spot as determined'by the photoelectric range-finder A, B, M. A series of contour lines are thus produced, which when viewed through the frame scanning mirror H appear to the eye in three dimensions. In a modified arrangement the image is projected on a viewing screen which is moved backward and forward in accordance with the frame scan. Various optical arrangements are described for use in scanning objects with suitable perspective and from different directions, and for providing colour. The first Provisional Specification also mentions the.use of the photoelectric range-finder for determining the ranges and speeds of moving objects, and refers to Specifications 557,837, [Group XX], and 562,168.