Patent ID: 8369201

Claim:
An optical pickup comprising: an optical system comprising: an object lens to illuminate a first light for performing information recording or information reproducing on a recording layer as a target and a second light different from the first light with respect to an optical recording medium, which includes a reference plane having a reflection film and the recording layer which is disposed at a layer position different from that of the reference plane and on which information recording is performed through mark formation according to light illumination; a focus-aligned position adjusting unit to adjust a focus-aligned position of the first light through the object lens by changing collimation of the first light incident to the object lens; and a focusing mechanism to drive the object lens in a focusing direction, which is a direction of approaching/separating with respect to the optical recording medium, wherein a depth of focus λ/NA 2 of the first light, defined by a wavelength λ of the first light and a numerical aperture NA of the object lens with respect to the first light, is denoted by α, a maximum surface blur range of the optical recording medium is denoted by D, the optical system is designed so that a use magnification ratio f 3 of the object lens with respect to the first light satisfies |β|≧√(D/α).