Patent ID: 7440154

Claim:
A Fourier transform lens system, comprising: a first lens group having positive power, wherein the first lens group comprises a first positive meniscus lens and a negative meniscus lens, and the first positive meniscus lens has a concave lens surface facing toward a concave lens surface of the negative meniscus lens; a second lens group having positive power, wherein the second lens group comprises at least one bi-convex lens, and the negative meniscus lens of the first lens group is adjacent to the second lens group; and a third lens group having negative power, wherein the third lens group comprises a second positive meniscus lens adjacent to the second lens group, and a bi-concave lens, the second positive meniscus lens has a convex lens surface facing toward the second lens group, and the first lens group, the second lens group, and the third lens group are arranged on a common optical axis of the Fourier transform lens system in that sequence; and wherein the Fourier transform lens system satisfies the following conditions (1)˜(4): (1) 0.8<f 2 /f<1.4, (2) −1.3<R 12F /f<−0.7, (3) 0.35<R 31F /f<0.75, and (4) 0.3<R 32R /f<0.7, where, f is the total focal length of the Fourier transform lens system, f 2 is the focal length of the second lens group, R 12F is the radius of curvature of the concave lens surface of the negative meniscus lens, R 31F is the radius of curvature of the convex lens surface of the second positive meniscus lens, and R 32R is the radius of curvature of a concave lens surface of the bi-concave lens which faces away from the second lens group.