| 摘要 |
PURPOSE:To obtain optimum exposure to an objective being a main objective, by applying only a video signal in the pickup range where the main objectives are much placed, to an automatic iris control circuit. CONSTITUTION:In applying a power supply, a triangle wave signal A in synchronizing with a vertical deflection period 1V is generated from an oscillator 1 and a DC bias is applied from a DC level varying circuit 2. This signal is compared with a reference value Vr at a comparator 4, and an exposure control range signal C is generated as a pulsive signal in the range exceeding the Vr. A gate circuit 7 passes a video signal D for iris control only when the signal C is generated. In this case, since the signal C is a pulsive signal having a width designated with a variable resistor 3 from the center of the vertical deflection, only the video signal in the range having a width being upper and lower direction from the center of the pickup range is used for the automatic iris control. |
