Patent ID: 8098564

Claim:
An objective lens for an optical pickup apparatus recording or reproducing information by converging a light flux with a wavelength λ 1 (380 nm<λ 1 <420 nm) emitted from a light source onto an information recording surface of an optical information recording medium, the objective lens consisting of: a single lens including at least one aspheric surface, wherein the objective lens satisfies following expressions: 2.0≦Φ≦4.0, 1.5 <n< 1.75 0.7 <d/f< 1.2, 0.8 <NA< 0.9, and −1.17 n+ 2.8 <d/f<− 0.59 n+ 2.0, where Φ (mm) is an effective aperture at a light source side of the objective lens, d (mm) is a thickness on an optical axis of the objective lens, f (mm) is a focal length of the objective lens, NA is a numerical aperture at an image side of the objective lens, and n is a refractive index of the objective lens for the wavelength λ 1 .