Objective lens for optical pickup apparatus

摘要

An optical pickup apparatus including an improved objective lens having at least one ring-shaped mask for preventing aberrations caused by differences in the thickness of discs being reproduced. The objective lens is capable of achieving improved focus by removing aberrations which occur when reading data from discs having different recording densities and thicknesses. The masks formed in the objective lens has a predetermined mask radius (rn+1) and a predetermined mask width ( DELTA rn+1).