AUTOMATIC FOCUSING DEVICE

摘要

PURPOSE:To attain accurate focusing operation even to an object with high brightness and low contrast by controlling the drive speed of a focus adjustment system based on an edge width detection of an object image and a displacement being the sum of a high frequency component to the edge width detection value. CONSTITUTION:An edge width detection output outputted from an edge width detection circuit 7 and a high frequency component outputted from a band pass filter 6 are summed. The detected values in the present and preceding fields of the sum are compared to obtain a difference D. The characteristic of the difference is zero at a focal point and the polarity is inverted before and after the focal adjustment. It is possible to detect a focal point where the sum if maximized by using the polarity inversion. A focusing lens drive motor 11 is driven at a low speed surely in any state at a prescribed range near the focal point and the motor is surely stopped at the focal point. Thus, highly accurate and quick focus is attained.