Patent ID: 7430159

Claim:
An optical pick-up used for recording data to and/or reproducing data from at least three types of optical discs having at least two different thicknesses of cover layers, comprising: light sources capable of emitting at least three light beams having different wavelengths, one of the at least three light beams being selectively emitted when one of the at least three types of optical discs is used; and an objective lens, wherein when a thickness of a first optical disc of the at least three types of optical discs to be used for recording data and/or reproducing data using a first light beam of the at least three light beams having a wavelength shortest of all wavelengths of the at least three light beams is represented by t 1 , a thickness of a second optical disc of the at least three types of optical discs to be used for recording data and/or reproducing data using a second light beam of the at least three light beams having a wavelength longer than that of the first light beam is represented by t 2 , and a thickness of a third optical disc of the at least three types of optical discs to be used for recording data and/or reproducing data using a third light beam of the at least three light beams having a wavelength longest of all of the wavelengths of the at least three light beams is represented by t 3 , a relationship t 1 ≦t 2 ≦t 3 is satisfied, wherein when a numerical aperture required for recording data to and/or reproducing data from the first optical disc is represented by NA 1 , a numerical aperture required for recording data to and/or reproducing data from the second optical disc is represented by NA 2 , and a numerical aperture required for recording data to and/or reproducing data from the third optical disc is represented by NA 3 , a relationship NA 1 ≧NA 2 >NA 3 is satisfied, wherein the first light beam is incident on the objective lens as a converging light beam, and the second and third light beams are incident on the objective lens as diverging light beams, respectively, wherein given that magnification of the objective lens is ml when the first optical disc is used, magnification of the objective lens is m 2 when the second optical disc is used, and magnification of the objective lens is m 3 when the third optical disc is used, following conditions are satisfied: m1>0 m3<m2<0.