| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system capable of writting and reading data to/from optical disks whose protective substrates are different in thickness. SOLUTION: The diaphragm aperture to be inserted into the optical path of this optical system is constituted selectably for a circular aperture 20 or a ring-band aperture 21. Then, at the time of performing the write or the read to/from an optical disk 30 having the protective substrate thickness of 1.2 mm, the circular aperture 20 is selected. At this time, the spherical aberration of an objective lens 10 is corrected with respect to the optical disk 30 having the protective substrate thickness of 1.2 mm. Besides, at the time of performing the write or the read to/from an optical disk 31 having the protective substrate thickness of 0.6 mm, the ring-band aperture 21 is selected and only the light transmitting the peripheral part of the lens 10 is used by the aperture 21. Thus, the spherical aberration to be generated by the difference of the protective substrate thicknesses is reduced. |
