| 摘要 |
PURPOSE:To perform automatic focusing without convergence of the focus position slippage detection laser light flux onto the information face of a video disc, by causing the light path distance from the convergence point of the focus position slippage detection laser light flux to the read lens main plane to differ from the corresponding light path distance of the information detection laser light flux. CONSTITUTION:Since distance l1 between lens main plane 6A and convergence point B for focus position slippage detection light flux 4b-1 is slightly longer than distance L1 between lens 6A and convergence point A for information detection light flux 4a-1, point C where focus position slippage detection light flux 4b-1 is converged by reading lens 6 is slipped to the front side of video disc 7. That is, light flux 4b-1 is not converged onto information face 7a of video disc 7, and the spot of this light flux on disc information face 7a becomes comparatively large diameter, and the recording signal on the disc is not disturbance to the focus position slippage control signal without reading of the tracking signal and the information signal. |
