| 摘要 |
PURPOSE:To prevent a reproduced picture from being dark due to stop excessively an iris even in case of back light by providing a converting circuit attenuating a signal at the part corresponding to the vertical upper part of a video signal, and controlling the iris by this converted output. CONSTITUTION:The light from an object field is made incident to an image pickup tube 3 through a lens 1 and an iris 2 and a video signal outputted from the image pickup tube 3 is inputted to a process circuit via an amplifier 4. Furthermore, the video signal from the amplifier 4 is fed to an upper part converting circuit 5 attenuating the signal part corresponding to the upper part of the object field and the converting signal is inputted also to an iris drive circuit 7 via a smoothing circuit 6. Even if a bright sky enters the upper part of the object field such as in case of light, since the corresponding signal part thereto is attenuated and the level of an input signal does not go too high, it is prevented that the iris 2 is stopped excessively and the part other than the bright part is made too dark.
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