| 摘要 |
In an aspherical lens element which has an optical axis, a focal length f, a thickness D along the optical axis, and first and second aspherical convex surfaces defined by first and second predetermined formulae represented as functions of first and second radii r1 and r2 of curvature at apexes of the first and the second aspherical convex surfaces and first and second coefficients k1 and k2 of cones, the aspherical lens element is formed by a low dispersion glass material which has a refractive index n and an Abbe number nu specified by: 1.44<n<1.55, and 75< nu <90. In addition, the aspherical lens element is defined by: 1.5<(f/D)<1.9, -0.4<(r1/r2)<-0.2, and 10<k1xk2-1000E1<30.
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