| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a lens unit wherein the imaging characteristic of the compatible type objective lens for a BD can be easily increased without complicating an assembly process. <P>SOLUTION: A center of an objective lens body 1 and a center of a diffraction lens 2 are made coincident with each other in an optical path extending in an optical axis OA1 direction of the objective lens body 1 utilizing markers M1 and M2. In this case, inclined angles of first and second surfaces 2a and 2b are 3° and a moving amount of the first surface 2a is 11 μm. In this state, coma aberration in 655 nm wavelength for a DVD caused by shift of the first surface 2a is +71 mλ, coma aberration caused by inclination of the first surface 2a is +35 mλ, and coma aberration caused by inclination of the second surface 2b is -105 mλ, and thereby coma aberration as the whole objective lens unit 50 is 0 mλ. Coma aberration generated as the objective lens unit 50 can be made nearly zero irrespective of a value of an inclined angle θ of the diffraction lens 2. <P>COPYRIGHT: (C)2011,JPO&INPIT |
