GB741592A - Improvements in or relating to television transmitting apparatus - Google Patents

Abstract

741,592. Television. PYE, Ltd. Sept. 8, 1952 [Sept. 6, 1951], No. 21084/51. Class 40 (3). Television transmitting apparatus of the type described in Specification 656,069, in which scanning of the target 8 of an image iconoscope is effected by a flying spot scanner 1 scanning the same area of the photo-cathode 6 as that on which the image 16, is projected, is arranged whereby a slide or kinematograph film 17 may be positioned in front of the flying spot scanner so that the apparatus can be operated either as a conventional flying-spot scanner or as a storage type pick-up tube. When operated normally, the light from the scanning spot is projected directly on to the photo-cathode together with the light from image 16, and the output is derived from across the target electrode resistor 12 through amplifier 14. When operating as a flying spot scanner, the slide or film 17 is positioned in front of scanner 1 and the light from image 16 is cut off. For this mode of operation, the pick-up tube functions as a simple photocell, the output being derived from the photocathode current collected by electrode 11. The current flows through resistor 18 and the fluctuations are amplified in amplifier 19. When operating as a flying spot scanner, the focus coil 10 is preferably not energized. By interposing a slide or film in the scanning light beam whilst the photo-cathode is simultaneously exposed to image 16 a composite signal may be derived from the target output. According to a feature of the invention, the target may be made semitransparent by the use of a mica sheet backed by a semi-transparent metallic film. By this means, the photo-cathode may be illuminated from the rear. Thus, as illustrated, a transparent slide 16<SP>1</SP> may be projected simultaneously or alternatively with image 16 or the film 17. This arrangement may be used for projecting captions during intervals between film transmission, switching means being operated upon starting up the film feeding mechanism to deenergize the focus coil. In a modified arrangement, Fig. 2 (not shown), the pick-up tube includes two electron multiplier arrangements constructed as described in Specification 721,943 and serving respectively to multiply the electrons released from the target and photocathode. The tube employed in this modified arrangement forms the subject-matter of Specification 741,649, [Group XL (a)].