| 摘要 |
PURPOSE:To enable automatic focusing positioning based on the detection of high precision by comparing an output signal corresponding to the projection image which makes returning light from a disk incident on the plural light receiving parts of a light receiving body with a reference signal corresponding to a gap. CONSTITUTION:In the case of the in-focusing state, the laser beam flux from a laser beam source is made incident on a disk 1 through an objective lens 2 as incident light 5A, and a projection image 6 due to the returning light 5 from the disk 1 is formed on a light receiving body 4, and an actuator 5 keeps the position. In the case of rear focus, the projection image 6 is enlarged and an addition output 10a is larger than a reference signal 11, therefore, a control signal 13a based on a comparison output 12a is sent to an actuator 4 and the objective lens 2 is moved to attain the in-focusing state. |
