Patent GB-1027884-A (GB)
Title: Improvements relating to devices for cinematographically recording the screen image of television display tubes
IPC: G03B31/02
Filed: 1963-11-01
Abstract: 1,027,884. Television. OPTISCHE INDUSTRIE " DE OUDE DELFT " N. V. Nov. 1, 1963 [Nov. 5, 1962], No. 43266/63. Heading H4F. A cinematrographic camera 3 driven by a synchronous motor 10 which cinematographically records the screen image of a television display tube 4 incorporated in a closed circuit television system which includes a master oscillator whose frequency is adjustable, comprises means to clamp in phase the field synchronizing signal derived from the master oscillator to a cyclically modulated electrical signal generated by the camera whose phase has a predetermined relation to the position of the driven shaft 7 of the camera. The camera 3 has a rotating blade shutter 6 mounted on shaft 7 and a lens 2 which projects the image of screen 4 on to the film 1. A disc-shaped element 11 whose opacity in circumferential direction varies sinusoidally is mounted on shaft 7 and a lens 12 projects on to disc 11 an image 13 of narrow slit 14 which is illuminated by a light source 15, the light which is transmitted by the disc being focused by lens 16 on to a photo-electric cell 17. The output signal of the photo-cell is a sine wave having a fixed phase relation to the position of the camera shutter 6. A phase detector 29 (Fig. 2, not shown), compares the phase of the field synchronizing pulses from the master oscillator to the phase of the sine wave signal from the photo-electric cell 17. If deviations from a predetermined phase relation occur, e.g. if the field synchronizing pulses do not coincide with the passages through zero of the sine wave, a control signal is fed back to the master oscillator which changes its frequency such that the phase difference is reduced to zero. According to the frame frequency of the camera a disc 11 is used which produces an appropriate number of full waves of the sine wave for each revolution. Shutter blade 6 has an exposure angle of 180 degrees and of each television picture only one field is filmed whereas the duration of the other field is used for feeding the film. In the embodiment described, each time the camera is used the master oscillator is first synchronized with the mains voltage and only after the motor 10 has arrived at its nominal speed is the system changed-over to shutter synchronization by means of a switch operated by a time relay. Instead of the optical method of generating the sine wave a switch in a D.C. circuit which is opened and closed by means of an arm on shaft 7 or a rotating magnet on shaft 7 which induces in a stationary coil an A.C. voltage may be used. The invention may be applied to cameras with a continuously or intermittently moving film with or without shutters. In a further embodiment a cinematographic camera is described which is adaptable to two frame frequencies and includes a rotating blade having a light transmitting sector smaller than 180 degrees and a light source and a corresponding photo-cell on each side of the motor shaft, the output signal of one or both of the photocells being used to derive the cyclically modulated reference signal.