Patent ID: 7817525

Claim:
An objective lens for converging light onto a recording surface of an optical information recording medium in order to perform at least one of recording, reproduction and deletion of information on the optical information recording medium, wherein the objective lens is a bi-convex single lens having at least one aspheric surface, and satisfies the following conditions: 3.5 <D H-S /D H-H′ <4.3 (1) 3.5 <D H′-T2 /D T1-H <50 (2) 0.9 <d/f <1.1 (3) (here, a numerical aperture NA on the optical information recording medium side of the objective lens satisfies NA≧0.85) where, D H-S is a distance [mm] on the optical axis from a front principal point H of the objective lens to a focal point S on an optical information recording medium side of the objective lens, D H-H′ is a distance [mm] on the optical axis from the front principal point H of the objective lens to a rear principal point H′ of the objective lens, D H′-T2 is a distance [mm] on the optical axis from the rear principal point H′ of the objective lens to an intersecting point T 2 of the optical axis and the optical information recording medium side surface of the objective lens, D T1-H is a distance [mm] on the optical axis from an intersecting point T 1 of the optical axis and a light source side surface of the objective lens to the front principal point H of the objective lens, d is a thickness [mm] on the optical axis of the objective lens, and f is a focal length [mm] of the objective lens.