| 摘要 |
PURPOSE:To prevent malfunction due to response of a lens by obtaining a signal having changed weight according to frequencies of output signals, and driving the lens to make the signal maximum. CONSTITUTION:The image of a subject is converted to electric signals by an image pickup element 2 and given to a differentiating circuit through a preamplifier 3. The circuit 13 compensates lowering in amplitude of frequency spectrum of output signals obtained from the element 2, and makes a ratio of high-frequency component to low-frequency component greater than a fixed value, and facilitates detection of change of high frequency components. As detection is made from low frequency to high frequency, malfunction caused by a response of the lens does not occur. With respect to an output of the circuit 13, a reference frequency component is detected by a reference frequency detecting circuit 8, and the reference frequency component is synchronously detected at the reference frequency by a synchronous detecting circuit 10 and the phase and amplitude are detected. The detection signal is given to a motor driving circuit 11 and focus matching of the lens 1 is performed. |
