| 摘要 |
PURPOSE:To control aperture independently and manually without receiving the limitation of an automatic gain control system, by fixing the gain of the automatic gain control system in response to switching of the aperture of an image pickup device to a manual mode from an automatic mode. CONSTITUTION:In an automatic diaphragm mode the light quantity of the optical information given from a subject increases or decreases greatly and the control is impossible for light quantity by means of an automatic light quantity control system. In such a case, an automatic gain control system connected to the next stage works to keep the output of a gain control amplifier 6 at a fixed level in place of said light quantity control system set at the preceding stage. When an automatic/manual changeover switch 16 is set to a manual mode, a diaphragm device 2 is put in a manual mode. Thus the aperture can be set manually at the optional value. A coupling switch 14 is opened as soon as the switch 16 is set in a manual mode. A voltage memory circuit 15 stores and preserves the DC voltage given from an integration circuit 7 immediately before the switch 14 is changed. This stored DC voltage is applied to the amplifier 6 to keep the gain of the circuit 6 at a fixed level.
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