| 摘要 |
PURPOSE:To stabilize diaphragm operation by setting an aperture value by the count value of a counter, and then providing a circuit which makes variation in the quantity of light per unit bit constant when converting the count value into the aperture value. CONSTITUTION:The aperture value of a diaphragm 2 provided to an image pickup tube 1 is adjusted by adjusting the size of an aperture 4 by rotating aperture blades by a motor 3 for aperture adjustment. Simultaneously, the slider 11 of a variable resistor 10 slides by coupling with the diaphragm 2. For automatic aperture adjustment, a switch 5 is opened and a switch 6 is closed. The output video signal of the image pickup tube 1 is sent through a preamplifier 7 to a trailing signal processing circuit, and a detecting circuit 8 detects the signal level. The detected voltage of the detecting circuit 8 is applied to a voltage comparing circuit 9, which compares the input with a reference voltage Vs. Its comparison voltage controls the motor 3 through a diode D2 to hold the aperture value of the diaphragm 2 constant according to the signal level. |
