Patent ID: 7054252

Claim:
An optical pickup for recording information on an optical recording medium and retrieving information from the optical recording medium by radiating a light beam on the optical recording medium comprising: a light source which emits the light beam; an object lens which converges the tight beam into a convergent light beam and directs the convergent light beam to a recording layer of the optical recording medium; and an aberration correction lens assembly between the light source and the object lens and including at least one movable lens which is movable in an optical axis direction, the aberration correction lens assembly controlling the movable lens to convert the light beam to one of a convergent light beam and a divergent light beam so as to correct spherical aberration, wherein a distance between a principal plane of the aberration correction lens assembly on a light emergent side and a principal plane of the object lens on a light incident side falls within a range determined in accordance with a numerical aperture of the object lens, a focal length of the aberration correction lens assembly on the light emergent side, and a focal length of the object lens, wherein the distance between the principal plane of the aberration correction lens assembly on the light emergent side and the principal plane of the object lens is determined by the following equation: ( f 2 + f 3 ) - 10 ⁢ f 3 2 ⁡ ( mm ) - 1 3 ⁢ N ⁢ ⁢ A 4 < e 2 < ( f 2 + f 3 ) + 10 ⁢ f 3 2 ⁡ ( mm ) - 1 3 ⁢ N ⁢ ⁢ A 4 where e 2 represents the distance between the principal plane of a lens in the aberration correction lens assembly on the most light emergent side and the principal plane of the object lens, NA represents the numerical aperture of the object lens, f 2 represents the focal length of the aberration correction lens assembly on the light emergent side, and f 3 represents the focal length of the object lens, wherein the numerical aperture of the object lens is not less than 0.80, and wherein the focal length of the object lens is not greater than 2 mm.