Patent ID: 8179769

Claim:
An objective lens for converging light on an information recording layer of an optical disc, the light being one of first light having a first wavelength, second light having a second wavelength that is shorter than the first wavelength, and third light having a third wavelength that is shorter than the first wavelength and is longer than the second wavelength, the objective lens comprising: an inner zone including an optical axis; a middle zone arranged in an outer peripheral area of the inner zone; and an outer zone arranged in an outer peripheral area of the middle zone, wherein: an effective diameter zone of the objective lens includes the inner zone, the middle zone, and the outer zone; when the first light passes through the inner zone in a diverging state, the first light is converged on an information recording layer of a first optical disc through transparent substrate having a thickness of t1; when the third light passes through the inner zone and the middle zone in a converging state, the third light is converged on an information recording layer of a second optical disc through transparent substrate having a thickness of t2; the second light passing through the effective diameter zone in generally parallel is converged on an information recording layer of a third optical disc through transparent substrate having a thickness of t3, where t1, t2, and t3 satisfy t1>t2>t3, and a focal distance f1 for converging the first light is longer than a focal distance f3 for converging the second light.