| 摘要 |
PURPOSE:To execute quickly an automatic focus control by constituting so that an objective in a video disk player is raised at a high speed in case when it is out of an automatic focus control leading-in range, and it is raised slowly in case when said lens is within a leading-in possible range. CONSTITUTION:A photodetector 6 detects a focus shift quantity, an objective driving mechanism 9 is driven by a phase compensating circuit 7 and an objective driving circuit 8, and a focus of a lens beam is controlled automatically. In case an objective approaches a prescribed value, a time consant switching circuit 14 of a starting oscillator 10 is operated, a time constant of the starting oscillator 10 is changed, and a raising speed of the objective is varied. Therefore, even when a variation of a relative distance of the disk surface and the objective at the time when a control loop is off is large, or even when a variation of a driving force of the lens is large, an automatic focus control device can be led in at a high speed and very stably. |
