| 摘要 |
PURPOSE:To facilitate the discrimination of a focal position by extracting only a high frequency component included in a video signal so as to apply peak detection and forming an automatic gain control loop so as to make the level of the high frequency component constant. CONSTITUTION:The gain control is applied so as to keep the high frequency component of a video signal constant through the forming of an AGC loop as AGC(automatic gain control) circuit 5 to high pass filter 6 to peak detection section 7 to comparator circuit 10 to AGC circuit 5. An output of the comparator 10 is sent to a focus control circuit 12 as an evaluation voltage. Thus, the dispersion due to contract of an object is suppressed relating to the evaluation curve for detecting a focus. Thus, the detection of the focus, that is, the detection of the peak of the evaluation curve is facilitated and an evaluation voltage with a sufficient level even to an object with an especially contrast is obtained. |
