Patent ID: 7924685
Filing Date: 2011-04-12
Classification: G11B

Abstract:
1. An objective lens for an optical pickup capable of recording or reproducing an optical information recording medium having a first layer recording layer with thin transparent board thickness t 1 and a second recording layer with thick transparent board thickness t 2 , wherein the objective lens has a numerical aperture which is equal to or higher than 0.81, and is made of a plastic material, and the objective lens includes a point at which a third order comma aberration amount generated at a time of a lens tilt of said objective lens becomes equal to a third order comma aberration amount generated at a time when a disc is tilted at the same angle amount as said lens tilt angle, in a transparent board thickness of t 2 +Δt (Δt>0) under a room temperature (25±3° C.).