Patent ID: 8576685

Claim:
An objective lens element which has, on an incident-side surface and on an exit-side surface, optically functional surfaces having rotational symmetry axes and which converges a light beam incident from the incident-side surface, wherein in a ring-shaped region of the optically functional surface on the exit-side surface outside an effective diameter, an outer peripheral portion which includes an outer edge of the objective lens and protrudes toward a spot side beyond a surface top of the optically functional surface is provided, and a rate of change in sag of the exit-side surface inside the effective diameter and a rate of change in sag of the exit-side surface of the outer peripheral portion are continuous across a region from the symmetry axis to the outer edge of the objective lens, the rate of change in sag of the exit-side surface being the derivative of sag with respect to the exit-side radius of the objective lens.