| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method of detecting a focal position deviation which is capable of exactly matching the focus of a beam-condensing optical system to an information recording layer of an optical recording medium by detecting the focal deviation of the beam-condensing optical system which has no offset. <P>SOLUTION: The focal position deviation of a two-element objective lens 9 is detected in accordance with the light beam passing a region 2b which is a region occupying 60 to 85% of the effective diameter of the beam determined by the aperture of the objective lens around an optical axis OZ of the light beam which has passed the two-elements objective lens 9. <P>COPYRIGHT: (C)2004,JPO&NCIPI |
