| 摘要 |
<p>A device for focussing a read-out light beam on a moving data carrier. It comprises an objective lens which causes said read-out beam to converge on the data carrier; a cylindrical lens arranged in the path of a light beam reflected by the data carrier; and photo-electric means for detecting the reflected beam and arranged in such a fashion that the light spot obtained there, normally substantially circular in shape, is distorded by elongation if focussing of the read-out beam on the data carrier is incorrect.</p> |
