[2] F Jun-liu, W Quan-ying, C Bao-hua, et al. An off-axis Go. lay3 spare aperture telescope with a freeform secondarymirror[J]. Optical Review, 2019, 26（3）: 310-318.
[4] Anzai S. Reflection type image forming optical system hav.ing a large angle of view[P]. US patent, 4037943, 1977.
[5] Hallam K L, Howell B J，Wilson M E. Wide-angle flat field telescope[P]. US patent, 4598981, 1986.
