Patent ID: 7664003

Claim:
An objective lens for use in an optical pickup apparatus for recording and/or reproducing information on a first optical information recording medium having a protective substrate with a thickness t 1 using a light flux with a wavelength λ 1 , for recording and/or reproducing information on a second optical information recording medium having a protective substrate with a thickness t 2 (t 1 <t 2 ) using a light flux with a wavelength λ 2 (λ 1 <λ 2 ) and for recording and/or reproducing information on a third optical information recording medium having a protective substrate with a thickness t 3 (t 2 <t 3 ) using a light flux with the wavelength λ 2 , the objective lens comprising: an optical surface including a central area and a peripheral area arranged at an outside of the central area, wherein the central area transmits a light flux with the wavelength λ 2 used for reproducing or recording information on the second optical information recording medium or the third optical information recording medium and the peripheral area transmits a light flux with the wavelength λ 2 not used for reproducing or recording information on the second optical information recording medium or the third optical information recording medium, the objective lens converges a light flux with the wavelength λ 1 on an information recording surface of the first optical information recording medium, converges a light flux with the wavelength λ 2 on an information recording surface of the second optical information recording medium, and converges a light flux with the wavelength λ 2 on an information recording surface of the third optical information recording medium, and when the objective optical lens forms the light flux with the wavelength λ 2 passing the central area into a converged spot through a substrate with a thickness t 4 (t 2 <t 4 <t 3 ), the objective optical lens makes a spherical aberration of the converged spot a minimum value, and the objective lens satisfies the following expressions: 0.60≦NA1≦0.67 0.45≦NA2≦0.55 where NA 1 is a numerical aperture of image side of the objective lens which is necessary for information reproducing or recording on the first optical information recording medium, and NA 2 is a numerical aperture of image side of the objective lens which is necessary for information reproducing or recording on the second optical information recording medium.