| 摘要 |
An objective lens has a numerical aperture of 8.0 or more and focusing a light beam of a wavelength λ of at least 450 nm or less on an optical information recording medium. In this objective lens, a wavefront-aberration deterioration level TOR, accumulative value of aberration deterioration, satisfies the equation (1): TOR=√{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}≦̸0.07[λrms]  (1) In the equation (1), TSA3 [λrm/μm] and TSA5 [λrm/μm] refer to a third-order thickness sensitivity level and a fifth-order thickness sensitivity level, which are generated when a thickness error from a predetermined thickness is +1 μm, respectively. DCm3 and DCm5 refer to a third-order decentering sensitivity level and a fifth-order decentering sensitivity level, which are generated when a decentering error of each of lens surfaces is 1 μm, respectively.
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