| 摘要 |
PURPOSE:To stabilize diaphragm operation by storing a storage element with an aperture value obtained in an automatic aperture adjustment state, and comparing the storage value at the point of the starting of aperture value locking with an aperture value after it. 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 interlocking 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 its 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 in accordance with the signal level. |
