| 摘要 |
<p>An automatic focusing system to focus automatically a light on an objective video-disk (4) where a P-N junction element, which is a light emitting portion (15) of a semiconductor light source (14), has a function of a pinhole board in order to avoid a difficult positioning of the pinhole board. The output of the semiconductor light source (14) is changed according to the strength of the light reflected from the surface of the video-disk (4). Hence, the output of the light source (14) is phase-detected in a phase detector (12) by comparison with the output of an oscillator (11), and the output of the phase detector (12) is supplied to an actuator (13), causing the automatic focusing of a lens. This system may be used in a video-disk reproducing apparatus. </p> |
