GB1243675A - Television camera arrangement - Google Patents

Abstract

1,243,675. Cathode - ray tube systems. FERNSEH G.m.b.H. 27 Nov., 1968 [27 Nov., 1967], No. 56358/68 Addition to 1,227,869. Heading H4T. In a colour television camera employing a plurality of pick-up tubes of the charge storage type together with dichroic elements supplying respective colour components of the image forming light to the photo-cathodes of each tube via respective secondary optical systems, light sources of controllable intensity are introduced between each such optical system and its associated tube to provide uniform illumination of the photo-cathodes. This illumination, which is additional to the image forming illumination, overcomes defects due to " persistence " in the photo-cathode of such tubes when operated at low brightness levels. Fig. 1 shows the general arrangement in which image light from a main objective lens 1 is directed via an intermediate objective lens 3 towards a beam splitting system comprising dichroic elements 4, 5 and mirrors 8, 11 and thence, as component colour beams (e.g. red, green and blue), via respective secondary objective lens systems 6, 9, 12 on to the photo-cathodes of pickup tubes 7, 10, 13. Between each secondary lens system and its associated tube the light sources, comprising four lamps (only three shown) 14, 15, 16 are positioned by means of the structure shown in Fig. 2, which comprises, for each source a ring member, 22, 23 fitted to the secondary lens systems and around the internal periphery of which the lamps (e.g. 24, 25) are arranged so as to illuminate a ring 26 of translucent, opalescent material which diffuses the light and produces uniform illumination of the photo-cathode of the pick-up tube 27. If desired, a screen or extensible bellows may be provided between the secondary lens and the tube to contain stray light. When the camera employs four pick-up tubes (i.e. three colour tubes and a luminance tube) the illumination of the photo-cathodes is effected by means of a lamp 37 (Fig. 3) the light from which is directed to the luminance tube 36 by reflection at the semi-silvered surface 33 of a beam splitter 32. The transmitted light is then reflected by a mirror 34 into an optical system 35 forming the intermediate lens system (such as lens system 3, Fig. 1) of the colour tube assembly.