| 摘要 |
PURPOSE:To ensure independent setting between the iris response time and the fade working time, by providing a means to use a fade control circuit and an automatic iris control circuit by switching. CONSTITUTION:The light put into a camera lens from a subject is controlled by an iris to a proper amount of light and then converted into an electric signal by a pickup tube to be connected to an input of a video signal amplifier VA. The DC voltage rectified by a diode D1 is charged/discharged and smoothed by resistances R1 and R2 plus capacitor C2 respectively. The response time of the iris is decided by the time constant of CR. A fade switch S1 is turned to ward R4 from R2, and thus the DC voltage at point A is charged to the capacitor C2 from a power source V4 via a resistance R5. Then the iris closes slowly to ensure a fade-out state. Then the switch S1 is set back at R2, and the DC voltage of a capacitor C3 is discharged by a resistance R3. Thus the DC voltage at point A is slowly reset to the original state to give a fade-in action. |
