GB986839A - Focussing aid - Google Patents

Abstract

986,839. Photoconductive devices. CANON CAMERA CO. Inc. Nov. 26, 1962 [Nov. 24' 1961], No. 44647/62. Heading H1K. [Also in Division H4] Various types of photoconductive cells are described in connection with a photo-electric focusing aid (see Division H4). Fig. 6 shows a cell comprising a plurality of mutually insulated parallel photoconductive strips 5, connected. in parallel by end electrodes t. The parallel strips are modified in Fig. 6<SP>1</SP> to a zig-zag shape, to increase the chance of an inevident light boundary between light and shade crossing the strips perpendicularly. Another modification is shown in Fig. 6<SP>11</SP> comprising two arrangements as in Fig. 6, back to back and mutually perpendicular. In the cell of Fig. 7 the strips S are in the form of mutually insulated sectors with central and circumferential electrodes. In the cell of Fig. 71 the strips in the cell of Fig. 6 have been bent into concentric annuli, whilst in Fig. 711 only one strip is used, wound into a spiral. In the cell of Fig. 8 the electrodes are in the form of interleaved combs forming a plurality of parallel broad strips. In the cell of Fig. 9, the photoconductive material is in the form of a disc S and the electrodes are in the form of front and rear discs, the front electrode being transparent or semi-transparent, e.g. a mesh. The photoconductive material may be cadmium sulphide and have a law relating its resistivity R‹ to the incident intensity of illumination I given by where k is a constant and e is a constant usually between 0.6 and 0.8.