GB1299288A - Improvements in or relating to pick-up tubes - Google Patents

Abstract

1299288 Image pick-up tubes ENGLISH ELECTRIC VALVE CO Ltd 2 July 1971 [30 July 1970] 36870/70 Heading H1D An image pick-up tube including a photoconductive target T such as a lead monoxide target, is provided with means for introducing light into the tubular anode G3 in an even manner round its circumference, the inner surface of the anode having light scattering properties so that it diffuses light over the rear surface of the target in order to increase dark current and thereby reduce build-up and decay lag at low light level operating conditions. The inner surface of the anode G3 is preferably roughened by chemical etching or by shot blasting. In one arrangement, Fig. 2, lamps 12 are arranged around the outside of the tube, and the envelope is provided with frosted portions 13 and 14 to guide the light; an aluminium disc R with a matt surface reflects light through the aper- tures 7 in the tapered portion of the anode. In another arrangement, Fig. 1 (not shown), the light source is internal and light is reflected from the envelope into apertures 7 via a diffuser ring of ground fused silica. In a modification, Fig. 3 (not shown), the diffuser comprises a silica ring arranged between two different diameter portions 4 and 5 of the anode. In a further arrangement, Fig. 4, light passes into the anode through perforations in a metal disc 16 which joins the two anode portions 4 and 5. In order to reduce the illumination at the centre of the target and thereby promote a more uniform dark current, aluminium may be evaporated from a position corresponding to the centre of the target through the perforated disc on to the diffuser D. If d is the diameter of the holes in the disc 16 the spacing a should be such that a/d=2(b/c), where b and c are the dimensions shown. The lamp 8 is preferably in parallel with the cathode heater H, but may alternatively have its own input connections. The envelope is coated with bands 9 and 10 of black and white paint the relative width of which can be varied in manufacture to adjust the amount of light reaching the diffuser ring D. A coating 11 of black paint prevents stray light reaching the front of the target.