Patent ID: 6900949

Claim:
An optical system of an optical pick-up for recording/reproducing data to/from a plurality of types of optical discs including a first optical disc having a relatively thick cover layer and a second optical disc having relatively thin cover layer, comprising: a plurality of light sources that correspond said plurality of types of optical discs; a first coupling lens that is used at least for said first optical disc; and an objective lens that is used for said plurality of types of optical discs, wherein said first coupling lens is located on a light source side of said objective lens, wherein a beam for said first optical disc emitted by one of said plurality of light sources passes through said first coupling lens and is incident on said objective lens as a diverging beam, the diverging beam being given spherical aberration by said coupling lens, wherein the spherical aberration of the diverging beam for said first optical disc and spherical aberration caused by said objective lens and a cover layer of said first optical disc cancel each other, wherein when said objective lens shifts in a plane substantially perpendicular to an optical axis of said objective lens, a coma component relating to the spherical aberration of the diverging beam which is shifted with respect to said objective lens is canceled by a coma generated by said objective lens and the cover layer of said first optical disc.