| 摘要 |
PURPOSE: To instantaneously fix an appropriate collimating lens at the position of a laser beam axis with reliable accuracy by linearly arranging two collimating lenses having different shapes and providing an electromagnetic movement mechanism on the one end. CONSTITUTION: When a conventional disk 9 is removed and a disk 14 with a half thickness is mounted, a changeover collimating lens 7a is moved to the direction of the arrow 13 in the collimating lens moving direction and fixed at the position of the laser beam axis in place of the conventional collimating lens 7. When the laser beam 3 is passed through the changeover collimating lens 7a, the aberration is changed like a changeover laser beam 3a, and the beam is focused on the signal recording surface of the disk 14 with a half thickness in the state the aberration is minimized after passed through an objective lens 8. |
