OBJECTIVE LENS

摘要

PURPOSE: An objective lens is provided to define a region of a ring-shape mask for an aberration amount by thickness changes of an optical disk as a numerical formula, to exactly set relations between a main beam and side beams generated by a generated aberration for a usable region of an optical pickup device. CONSTITUTION: A ring for intercepting a beam is formed on a concentric circle. The ring has a regular width by a formula on the basis of each diameter in two parts having diameters on an objective lens(L). Thus, a focus servo is stabilized.