| 摘要 |
A light-converging optical system has an objective lens arranged at a position to be opposite to an 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. 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: <?in-line-formulae description="In-line Formulae" end="lead"?>P<SUB>T1</SUB><P<SUB>T0</SUB><P<SUB>T2</SUB>, or P<SUB>T1</SUB>>P<SUB>T0</SUB>>P<SUB>T2</SUB>,<?in-line-formulae description="In-line Formulae" end="tail"?> where P<SUB>T0</SUB>, P<SUB>T1 </SUB>and P<SUB>T2 </SUB>are the total paraxial power (mm<SUP>-1</SUP>) of the aberration correcting element under the temperature of 25° C., -5° C. and 55° C. respectively.
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