| 摘要 |
PURPOSE:To make the focus adjustment highly accurate by interposing an optically transparent element having a variable thickness between an optical lens and a focal plane of a video disc recording and reproducing apparatus. CONSTITUTION:A reading laser beam 1 is concentrated by an optical lens 2 to concentrate a focal point on a video disc plane 3. Optically transparent elements 4a and 4b, which are interposed between the lens 2 and the plane 3, are made slidable relative to each other so that their thicknesses in the direction of the optical axis are varied to shift the focal plane of the lens 2. As a result, in accordance with the vertical changes in the plane 3, the transparent element 4a is shifted so that the focal point can always be formed on the plane 3. |
