GB608939A - Improvements in transmitting apparatus for the television of motion-picture film - Google Patents

Abstract

608,939. Television transmitters. GENERAL ELECTRIC CO., Ltd., and JESTY, L. C. Oct. 23, 1944, No. 20490. [Class 40 (iii)] In television transmitting apparatus of the kind in which a continuously moving film is scanned interlacedly by an electronic scanner, means are provided to compensate for imperfect interlacing due to shrinkage and, or, expansion of the film. Frame synchronizing pulses from terminal 10 control a saw-tooth generator 12 at frame frequency and a square-wave generator at half this frequency, Figs. 1 and 3. These waveforms are shown at (b) and (a) respectively, Fig. 2. The output from 14, through the potentiometer 15, is applied to the deflecting coils 16 in parallel with the outputs from 12 and when these two outputs are of equal value the waveform of the current through 16 is as shown in full lines in Fig. 2 (c). When film shrinkage occurs, perfect interlacing on alternate frame scans is brought about by adjustment of 15 so that the amplitude of 20<1> becomes 20<11>. Alternatively, the frequency of the saw-tooth wave generated by 12 may be halved and its amplitude doubled, the output of 14 normally being zero except when shrinkage occurs when it is increased from zero and in opposite phase to Fig. 2 (a) by a suitable amount. Means in which variation in the film length causes movement of an idler roller may be utilized to produce an indication of shrinkage and/or automatic adjustment of 15. In an alternative arrangement, Fig. 3, providing automatic compensation for film length variation, two electric pulse trains are produced by photo-electric cells 35, 38, co-operating with light sources 31, 32, which are modulated by the passage of the filmsprocket holes. The outputs from the photoelectric cells after amplification and limiting are fed to a phase discriminator 43 giving a D.C. output voltage which is zero when the pulse trains are in phase and increases with increasing phase difference. The D.C. voltage is applied as a control voltage to an attenuator 44 which fulfills the same function as resistor 15 in Fig. 1. The attenuator may comprise a variable Á thermionic valve, the gain of which is controlled by the D.C. voltage from 43. Instead of electronic compensation, movement of the sprocket 24, Fig. 3, may be transmitted by suitable means to the control member of 15, Fig. 1. When a cathode-ray tube employing electrostatic deflection is used the wave-forms shown at Fig. 2 will be those of voltage and not current, the outputs of 12 and 14 being then connected in series.