| 摘要 |
PURPOSE:To obtain a lightweight and miniaturized autofocusing device having simple constitution by forming an optical system fixing its front lens group to execute focusing by means of a master lens group or a part of the lenses, adopting aspheric lenses consisting of a plastic material for both the lens groups and allowing a focusing function to execute autofocusing operation. CONSTITUTION:A periodical signal for slightly oscillating the master lens group in the optical axis direction is sent to a motor 26 by an autofocusing (AF) circuit 25. At that time, an extraction signal extracting a high frequency component from a video signal obtained by an image pickup element 21 has fixed relation to a focusing state and the position of the extraction signal against a focused point can be decided by detecting the oscillating direction of the lens position and the changing direction of the high frequency component. When the variation of the high frequency signal is a certain value or less at the time of focusing decision, focusing is acknowledged, and when the focusing motor 26 is driven by the high frequency component signal, an inner master 17 is rotated by an output shaft of the motor 26 through a decelerating mechanism. Consequently, the miniaturized and lightweight autofocusing device capable of allowing the focusing lens to execute AF operation by a video signal is obtained. |
