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US 7,924,685 B2Granted
Objective lens
AssigneeHitachi Maxell, Ltd.
InventorsYasuyuki Sugi, Mitsuhiro Miyauchi, Mitsuru Ito, Naofumi Ueda
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AssigneeHitachi Maxell, Ltd.
InventorsYasuyuki Sugi, Mitsuhiro Miyauchi, Mitsuru Ito, Naofumi Ueda
Estimating the term…
An object of the invention is to provide a plastic objective lens having a good lens tilt property in both thicknesses of a two-layer disc in a used temperature range even in the plastic objective lens in which a numerical aperture (NA) is equal to or higher than 0.81, while dissolving the problem mentioned above. The objective lens includes a point at which a third order comma aberration amount generated at a time of a lens tilt of the 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 the lens tilt angle, in a transparent board thickness which is thicker than a larger thickness of the two-layer transparent board under a room temperature (25±3° C.).
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 t1 and a second recording layer with thick transparent board thickness t2, 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 t2+Δt (Δt>0) under a room temperature (25±3° C.).
An optical pickup device comprising:
Dependencies are inferred from the claim text.