| 摘要 |
PURPOSE:To make only normal photographing possible by detecting the presence of video signals and synchronizing signals, and driving a shutter to make photographing impossible when it is judged there is no signal. CONSTITUTION:An operation signal of a shutter 12 becomes effective only when a horizontal synchronizing signal, a vertical synchronizing signal and a video signal are detectable, and a controller 9 controls a filter 15 and film 17 by the shutter operation signal. When the operation signal of a shutter 20 is inputted to a driving device 12, the horizontal synchronizing signal, vertical synchronizing signal and video signal are detected by a signal detector 8, and the shutter is turned on only when above-mentioned signals are inputted simultaneously. When it is judged that even one of the signals is not inputted, the shutter is not made on, and an alarm is given by a buzzer 19, and at the same time, the kind of alarm is displayed by a displaying circuit 18. Thus, by detecting and controlling the horizontal synchronizing signal, vertical synchronizing signal and video signal necessary for display of CRT, exposure of a film can be prevented by controlling the operation of the shutter when normal video is not displayed on CRT.
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