| 摘要 |
PURPOSE:To completely detect the position of a focused point without increasing so much the overall focus searching time, by slowing down the moving speed of an objective lens after detecting by a detecting means that the objective lens is set at a point close to the focused point. CONSTITUTION:The rectangular wave delivered from an oscillation circuit 1 is applied to an integration circuit 2 consisting of a resistance R and a capacitor C1. Then a focus search drive signal having big gradient is obtained from the circuit 2 and applied to a driving coil for objective lens. A speed changing means 4 is provided with a switch S and a capacitor C2. The gradient of the focus search drive signal is reduced after the switch S is closed. Under such conditions, the focus error signal can detect more completely a focused point position (b) and however the focus searching period is slightly increased. |
