Patent ID: 7133332

Claim:
A light-converging optical system for recording and/or reproducing for an optical information recording medium to converge a light flux emitted from a light source onto an information recording plane of the optical information recording medium, comprising: an objective lens arranged at a position to be opposite to the optical information recording medium and including at least one plastic lens, and an aberration correcting element provided on an optical path between the light source and the objective lens and structured by two groups of a positive lens and a negative lens both being a plastic lens; wherein at least one of the positive lens and the negative lens has at least one diffractive surface on which a diffractive structure is formed and a total paraxial power of the aberration correcting element has a temperature dependency satisfying a formula of: P T1 <P T0 <P T2 , or P T1 >P T0 >P T2 , where P T0 is the total paraxial power (mm −1 ) of the aberration correcting element under the temperature of 25° C., P T1 is the total paraxial power (mm −1 ) of the aberration correcting element under the temperature of −5° C., and P T2 is the total paraxial power (mm −1 ) of the aberration correcting element under the temperature of 55° C.