| 摘要 |
An objective lens used for an optical information recording/reproducing apparatus for an optical disc based on a predetermined standard is made of resin and has a numerical aperture larger than or equal to 0.75. When f (unit: mm) represents a focal length at a wavelength λ (unit: nm), d (unit: mm) represents a thickness, and n represents a refractive index of the objective lens at the wavelength λ, the objective lens satisfies following conditions: 1.00<f<1.50  (1) 1.55<d·n/f<1.82  (2). At least a light source side surface of the objective lens is an aspherical surface. The objective lens satisfies a following condition: 2.80<(SAG1)′MAX·n<4.10   (3), where (SAG1)′MAX represents a maximum gradient of a gradient (SAG1)′ of a sag amount SAG of the aspherical surface at the light source side within an effective beam diameter.
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