| 摘要 |
PROBLEM TO BE SOLVED: To provide an objective lens for an optical disk, which is composed of a single lens having the number of openings of 0.7-0.8 and can cope with the optical disk having a thin reproducing transmission layer <=0.3 mm and has the following characteristics (i)-(iv) for a light having the wavelength in the order of 400 nm. (i) Eccentricity between both surfaces of the lens produced is tolerable. (ii) The satisfied aberration characteristics is provided on the axis. (iii) The deterioration of the aberration characteristics is a little on the off-axis. (iv) Operational distance is extensive (0.3 mm or larger is preferable). SOLUTION: This objective lens for the optical disk is the single lens having at least one surface formed to the aspherical shape and the number of openings 0.7-0.8, and is provided with the special features satisfying the following conditions. (1) 0.85<d/f<1.5, (2) 0>d/R2>-0.5, (3) n>1.6, where f is a focal distance of the lens, d is a center thickness of the lens, R2 is a radius of curvature on a vertex of the lens at the optical disk side, and n is a refractive index of the lens. |
