| 摘要 |
PROBLEM TO BE SOLVED: To provide a lens for an optical disk which is composed of a single lens of >=0.78 in numeric aperture and adaptive to an optical disk having a thin reproduction transmission layer of about <=0.3 mm and has characteristics (i) to (iv) to a light having a wavelength of about 400 nm; (i) the eccentricity tolerance between both the surfaces of the lens being within a manufacturable range, (ii) an excellent on-axis aberration characteristic being obtained, and (iii) deterioration in off-axis aberration characteristic being small. SOLUTION: This objective is a single lens which has at least one aspherical surface and a >=0.78 numerical aperture and an objective for an optical disk which meets the specific conditions. Namely, (1) d/f>1.2, (2) 0.65<R1/f<0.9, and (3) |R1/R2|<0.6, where (f) is the focal length of the lens, (d) is the center thickness of the lens, R1 is the radius of curvature of the lens at the vertex on a light source side, and R2 is the radius of curvature of the lens at the vertex on an optical disk side. |
