Patent ID: 7274646

Claim:
An object lens for an infinite-type optical pickup which performs recording, reproducing or deletion of information on an optical recording medium having an incident side substrate with a thickness of 0.1 mm with a beam having a wavelength of 407±10 nm, wherein: said object lens is used for focusing the beam onto a recording surface of the optical recording medium through the incident side substrate thereof so as to form a light spot on said recording surface so as to perform the information recording/reproducing/deletion; said object lens has a configuration of a single lens, with aspherical surface on each of both sides thereof, and has a numerical aperture NA falling within a range of 0.85≦NA; and said object lens has a configuration satisfying the following conditional formulas: R 1 /f≦ 1.0 nd− 0.7 (21) WD/f≦ 0.33 nd− 0.18 (22) where: R 1 denotes a paraxial curvature radius of the surface on the light source side; WD denotes a working distance; nd denotes a refractive index of the lens material with respect to the d-line; and f denotes the focal length.