| 摘要 |
<p>This invention relates to an improvement in a video signal playback device which derives video signals from a track on a video disc using a light source impinging upon an information track on the surface of the video disc, the light beam modulated by the information track being sensed in a light sensor. In prior art devices, poor picture quality has resulted from the fact that focus of the beam on the information track cannot be maintained dynamically, that is as the turntable rotates and the disc and read head move relative to one another radially of the disc. The present invention overcomes the deficiencies of the prior art in this respect by providing a reader and disc arranged for relative lateral movement radially of the disc wherein an objective lens mounted in the disc reader adjacent the disc maintains focusing of the light beam on the information track of the disc as the disc is played. The objective lens is mounted for movement relative to the surface of the disc along the path of impinging light beam to maintain focus of the beam on the information track as the rotating disc moves laterally relative to the reader.</p> |
