Patent GB-1466273-A (GB)
Title: Arrangement for controlling the vertical deflection of a flyin spot tube
IPC: H04N3/36
Filed: 1974-06-25
Abstract: 1466273 Film scanning THOMSON-CSF 25 June 1974 [26 June 1973] 28207/74 Heading H4F Correct scanning of the film 7 in a gate 5, Fig. 1, by light from a flying spot scanner 1 is controlled by deflecting the flying spot scanner beam at right angles to the line scan direction during each line blanking period so that at least part of the light from the scanner 1 is incident on one of the perforations of the film 7 to produce a signal which is used to control the flying spot scanner 1 to correctly position the beam at right angles to the line scan direction. In one embodiment frame scan of the film in gate 5 is provided by an oscillating mirror 3, Fig. 1, having a central groove (30, Figs. 2, 3, not shown) with its reflective surface inclined to the reflective surface of the rest of the mirror 3 to reflect part of the light from scanner 1 to a gate 51 via a mirror 4. A line scan L at gate 51 traverses a target 53, Fig. 4, having transparent slots 54, 55, 56, the deflected part of the scan being incident on a perforation 70. A detector circuit 8 successively produces, for each line scan, a pulse derived from perforation 70 and pulses derived from slots 56, 55, 54 which are passed to a control circuit 9 which supplies, via a circuit 10, a correcting signal to a circuit 11 controlling scanner 1. Control circuit 9 may include a switching circuit 100, Fig. 5, providing the pulses derived from the perforations to circuits 110, 125 and the pulses derived from the slots 56, 55, 54 to a. separating circuit 101. Each pulse derived from slot 56 controls the production at 103 of a sawtooth signal which is sampled at 102 by the respective pulse derived from slot 55 to produce a signal E 1  representative of the position of the respective line scan on target 53, which is compared at 106 with a reference signal R 1  produced by sampling at 104 a reference line frequency sawtooth signal produced at 105 by the respective pulse derived from slot 56. Comparator 106 is controlled by the respective pulse derived from slot 54 and provides an output to an AND gate 126 fed with line-frequency signals and providing the output of control circuit 9. Each pulse derived from a perforation samples at 110 a line frequency sawtooth signal produced at 112 to provide a signal E 2  representative of the perforation position, which is compared at 113 with a reference signal R 2 . Change over from detection of one perforation to detection of the following perforation occurs between the two interlaced fields scanning one film frame and a sampling circuit 111 detects any resulting change in signal E 2  to provide a signal to circuit 112 to compensate for irregularity in perforation spacing. The output signals from comparators 106, 113 are fed to a comparator 120 whose output is fed via an AND gate 121 to a storage circuit 122, circuits 121 and 122 also receiving the pulses derived from the perforations and delayed by a circuit 125. Storage circuit 122 provides an offset voltage to circuit 104 to control reference signal R 1  and to an adder 124 to control reference signal R 2 . If a perforation is correctly positioned but the scanning line L is incorrectly positioned with respect to the perforation and the target 53 the comparators 106, 113 produce equal outputs, comparator 120 produces a zero output, and the output of comparator 106 is passed via gate 126 to the circuit output. If a perforation is incorrectly positioned but the scanning line L is correctly positioned with respect to the target 53 comparator 106 produces a zero output whereas comparators 113 and 120 produce outputs, the output of comparator 120 causing a change in reference signal R 1  to produce an output from comparator 106 to control scanner 1 and also causing a change in reference signal R 2  so that the outputs of comparators 106, 113 are equal.  The slot 55 of target 53 may be replaced by a reference scale. In an alternative embodiment (Figs. 6, 7, not shown) the perforations are detected at the film gate 5, the resulting pulses being used to sample a line frequency sawtooth signal, the sampled signal being compared with a reference signal obtained by sampling a field frequency sawtooth signal by delayed line synchronization pulses.