Patent ID: 8228777

Claim:
An objective lens for an optical pickup, having a numerical aperture of 0.8 or more and focusing a light beam of a wavelength λ of 450 nm or less on an optical information recording medium, wherein a wavefront-aberration deterioration level TOR, a cumulative value of aberration deterioration, satisfies the following equation (1): TOR=√ {square root over (2.5 2 ( DCm 3 2 +DCm 5 2 )+( TSA 3 2 +TSA 5 2 ))}{square root over (2.5 2 ( DCm 3 2 +DCm 5 2 )+( TSA 3 2 +TSA 5 2 ))}≦0.07[λrms] (1) wherein: TSA3[λrms/μm] refers to a third-order thickness sensitivity level which is a third-order spherical aberration level generated when a thickness error from a predetermined thickness is +1 μm, TSA5 [λrms/μm] refers to a fifth-order thickness sensitivity level which is a fifth-order spherical aberration level generated when the thickness error from the predetermined thickness is +1 μm, DCm3 refers to a third-order decentering sensitivity level which is a third-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm, and DCm5 refers to a fifth-order decentering sensitivity level which is a fifth-order coma aberration level generated when a decentering error of each of lens surfaces is 1 μm.