Optical design of catadioptric LLL night vision objective

A design of low-light-level(LLL) night vision objective with long focal length and high relative aperture is introduced. The design parameters are as follows: the effective focal length is 100mm, the F-number is 1.4 and the field of view is 10.To improve the visual range, reduce the size and weight of the objective and get achromatic result in wide spectral range, the all-spherical catadioptric structure is selected. Catadioptric system is considerably shorter and lighter than the refractive lens with the same focal length and F-number. The Mangin mirror is introduced into the design, which gives the optical system extra degrees of freedom without adding another element. By optimizing the aberrations, good image quality of the objective is obtained. At the spatial frequency of 50lp/mm, the on-axis modulation transfer function (MTF) of the objective is not less than 0.4 and the off-axis MTF is not less than 0.2, which match with the limiting resolution of image intensifier. The distortion of objective is less than 2% in full field of view, and the total length of objective is 68mm.