Fourier lens system with low cost and large numerical aperture

The invention provides a Fourier lens system, comprising a double concave lens, a first convex lens and a second convex lens in sequence along the optical axis direction from object plane to image surface; wherein, the air gap between the double concave lens and the first convex lens as well as the air gap between the first convex lens and the second convex lens along the optical axis are less than 20mm. The Fourier lens system disclosed by the invention has large numerical aperture and angle field and compact structure; only spherical lenses or planar lenses are adopted without introducing non-spherical lens, thus reducing the difficulty of processing, testing and erecting and aligning of the lens, and further reducing the manufacturing cost of the lens.