| 摘要 |
PURPOSE:To form a miniaturized and lightweight condenser lens for an optical memory with efficient image formation by displaying an aspheric surface based on a specific formula and satisfying prescribed conditional equation. CONSTITUTION:When it is defined in a single lens 1 having a face opposed to a light source and a face on the opposite side respectively constituted of aspherical surfaces that a distance between a point on the spherical surface having high H from an optical axis and a contact plane on the vertex of the aspherical surface is X, the radius of curvature on the base curve of the nu-th face (nu=1, 2) is Rnu, the conical constant of the aspherical surface of the nu-th face (nu=1, 2) is Knu, and the aspherical factor of the aspherical surface on the nu-th face (nu=1, 2) is Anui (i=1-m), the aspherical surface can be expressed by an equation I and the conditions of inequalities II are satisfied. Provided that F is the focal distance of the lens, WD is a working distance, (t) is the thickness of protection layer on a memory using the lens, and (n) is a refractive index in used wavelength.
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