An optical system of an optical pick-up for a plurality of types of optical discs
with a corresponding plurality of light sources. A first coupling lens that is
used at least for the first optical disc, and an objective lens that is used for
the plurality of types of optical discs. A beam for the first optical disc emitted
by the plurality of light sources passes through the first coupling lens and is
incident on the objective lens as a diverging beam. The diverging beam being given
spherical aberration by the coupling lens. When the objective lens shift occurs,
a coma component relating to the spherical aberration of the diverging beam which
is shifted with respect to the objective lens due to the shift of the objective
lens is canceled by a coma generated by the objective lens and the cover layer
of the first optical disc.
