Patent ID: 7142374
Filing Date: 2006-11-28
Classification: G02B

Abstract:
1. An optical system for a riflescope comprising an objective lens group, an eyepiece lens element defining an optical axis with the objective lens group, and an erector lens group positioned between the objective lens group and the eyepiece lens element, the eyepiece lens element comprising an aspheric element having a diffractive configuration and combining with a spherical lens; wherein, the diffractive configuration of the aspheric element faces the erector lens group, and the aspheric element satisfies the following equation: where: Z is Sag value along the optical axis, c is the curvature (1/radius) of the surface, H is the semi-diameter height, K is the conic coefficient, and A, B, C and D are the 4 th -order, 6 th -order, 8 th -order and 10 th -order aspheric coefficients, respectively; wherein the eyepiece lens element satisfies the following condition: 3<S/F<4, where F is the focal length of the eyepiece lens element and S is the incremental sag of the aspheric element at a clear aperture of the eyepiece lens element.