| 摘要 |
PURPOSE: An object lens for an optical disk is provided to superior in a best image surface chromatic aberration characteristic and out-of-axis aberration characteristic and have a moderate eccentricity tolerance. CONSTITUTION: An objective lens(21) for an optical disk(23) includes a bi-aspherical single lens having a numerical aperture of 0.7 or more, wherein a center thickness of the lens is more than a focal distance. The optical-disk objective lens(21) is a bi-aspherical single lens with two aspheric surfaces generally having a design reference wavelength shorter than 450 nm, a numerical aperture of 0.7 or more, and a center thickness(D) of the lens(21) more than a focal distance. In further detail, the design reference wavelength of the objective lens(21) is set to 405 nm. Moreover, the numerical aperture(NA) of the objective lens(21) is designed to 0.75. Furthermore, the focal distance of the objective lens(21) is 2.5 mm, and an image forming magnification in the design reference wavelength of 405 nm is 0 times. Additionally, when an eccentricity delta between a first surface(S1) and a second surface(S2), i.e., a distance between a geometric center axis a1 of the surface(S1) and a geometric center axis(a2) of the surface(S2), is 5um an aberration is designed to be 0.03 λ or less.
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