| 摘要 |
PURPOSE:To always obtain an accurately just-focus condition by closing a focus-servo control loop as well as driving an entire optical system to detect a just-focus point when the entire optical system enter a focus-servo retracting area in the focus-servo retracting operation. CONSTITUTION:A detection level (a) is set first in the region with a decreasing tendency in focus error signals. Detection of this level means that the system is traveling in this region. Then, another level (b for example) is set in the region in which focus-servo retraction is possible. Detection of this level means that the system has just entered the region with an increasing tendency and servocontrol operation starts to control the system to be brought in the just- focus point. Upon detection, which is carried out by a CPU25, of the level, a focus-on signal is delivered from port B(30) to turn on a switch circuit 14 and start the focus-servo operation. A true just-focus point is detected by taking advantage of the output voltage of the low-pass filter 9 which is a voltage of the detected total quantity of the light. The voltage of detected total quantity of the light has the maximum value at the just-focus point.
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