GB859030A - Photographic recording of television pictures - Google Patents

Abstract

859,030. Television. BRITISH BROADCASTING CORPORATION. Oct. 22, 1959 [Sept. 26, 1958], No. 30877/58. Class 40(3). Relates to apparatus for recording television pictures produced on a cathode-ray tube screen 11, Fig. 1, with the aid of an intermittent motion film camera 10 which has a pull-down time greater than the television field blanking interval, the camera shutter being timed so as to open at a time subsequent to the start of each field, as illustrated in Fig. 2 at (a) and (b), and the tube screen having a persistence such as to permit recording of that part of field which is scanned before the shutter opens. According to the invention, the variation in picture intensity in the frame scan direction due to fading, which at the instant of opening the shutter takes the form shown in Fig. 2(c), together with the variation due to differing exposure times of those parts of the image scanned after opening the shutter, are compensated by the provision of an optical filter 18 graded in density in the frame scan direction in the manner shown in Fig. 2 (d). The filter may be placed against the tube screen, as illustrated, with the interposition of an optical cement or liquid 19 having a refractive index intermediate those of the glass face of the tube and the filter material. Alternatively the filter may be located inside the camera close to the image on the film. The camera pull-down operation is correctly timed with the television fields by means of a drive unit 15 which is fed with field synchronizing pulses and pull-down indication pulses. For recording interlaced television pictures the pull-down is arranged to occur during every alternate operation of the shutter, i.e. once for every two television fields.