Patent ID: 7260048

Claim:
An object lens for an optical pickup, said object lens being of finite conjugate type for use in an optical pickup having a unit, in which a semiconductor laser diode array including light emitting portions for respectively emitting light of different wavelengths, a photo detector and said object lens are integrated so that a relative positional relationship between said object lens and said semiconductor laser diode array is fixed, and capable of recording data in and reproducing data from a first optical recording medium and a second optical recording medium respectively having recording faces at different heights, optical paths from said light emitting portions for respectively emitting light of different wavelengths to the object lens being the same regardless of wavelength, a distance from the light outgoing face of the object lens to the surface of said first and second optical recording mediums in an optical system being changed by moving said unit entirely, and curvatures and aspheric coefficients of said object lens being defined so that said object lens has a plurality of numerical apertures to be changed in accordance with switching between said different wavelengths, whereby allowing said laser beam to be focused on said first optical recording medium or said second optical recording medium.