| 摘要 |
PURPOSE:To reduce wear and trouble and to prolong dramatically a service life by giving to a optical path length changing means a translucent member whose optical path length is changed due to properties. CONSTITUTION:When the voltage of a reference frequency signal from a frequency divider 20 is impressed on a translucent electrostriction member 13, said reference frequency changes the thickness of the translucent electrostriction member 13 to vary the optical path length. Accordingly, the focus of an object image formed by a photographing lens advances and retreats in the optical axis direction with respect to the image pickup surface of an image pickup tube 14. Namely, when the signal voltage at the reference frequency is impressed on the translucent electrostriction member 13, the focus of the object image with respect to the image pickup surface is changed back and forth without a mechanical movable part, and a pre-pin state and an after-pin state are detected. As a result, the constitution is simplified, and there is no trouble due to wear. Besides, the automatic focus adjusting device can be obtained which acts at a high speed with less power consumption. |
