Patent ID: 8406111

Claim:
An objective lens for use in an optical pickup apparatus comprising an objective lens, for forming a converged spot on an information recording surface of a first optical disc including a protective layer with a thickness t 1 by using a first light flux with a wavelength λ 1 (λm) emitted from a first light source, for forming a converged spot on an information recording surface of a second optical disc including a protective layer with a thickness t 2 (t 1 ≦t 2 ) by using a second light flux with a wavelength λ 2 (λ 1 <λ 2 ) emitted from a second light source, and for forming a converged spot on an information recording surface of a third optical disc including a protective layer with a thickness t 3 (t 2 <t 3 ) by using a third light flux with a wavelength λ 3 (λ 2 <λ 3 ) emitted from a third light source, wherein the objective lens is formed of a single lens, an optical surface of the single lens comprises a central area whose center is located at an optical axis, a peripheral area in a ringed shape formed around the central area, and a most peripheral area in a ringed shape formed around the peripheral area, the first light flux which has passed through the central area, the peripheral area and the most peripheral area is converged on the information recording surface of the first optical disc, the second light flux which has passed through the central area and the peripheral area is converged on the information recording surface of the second optical disc, and the second light flux which has passed through the most peripheral area is not converged on the information recording surface of the second optical disc, the third light flux which has passed through the central area is converged on the information recording surface of the third optical disc, and the third light flux which has passed through the peripheral area and the most peripheral area is not converged on the information recording surface of the third optical disc, the most peripheral area is a refractive surface, and the objective lens satisfies all of the conditional expressions (1) to (3), where m 1 is an image-forming magnification of the objective lens when information is reproduced and/or recoded for the first optical disc, m 2 is an image-forming magnification of the objective lens when information is reproduced and/or recoded for the second optical disc, m 3 is an image-forming magnification of the objective lens when information is reproduced and/or recoded for the third optical disc, WD 1 (mm) is a working distance of the objective lens when information is reproduced and/or recoded for the first optical disc, WD 2 (mm) is a working distance of the objective lens when information is reproduced and/or recoded for the second optical disc, and WD 3 (mm) is a working distance of the objective lens when information is reproduced and/or recoded for the third optical disc: −0.02≦ m 1≦0.02 (1) 0≦( WD 1 −WD 2)≦1.57 m 2+0.123 or 1.57 m 2+0.24≦( WD 1 −WD 2)≦0.7 (2) 0≦( WD 1 −WD 3)≦1.79 m 3+0.333 or 1.66 m 3+0.508≦( WD 1 −WD 3)≦0.7 (3).