Proceedings Article | 27 March 2022
Xiao Chen, Yu Bai, Hong-yu Wang
KEYWORDS: Zoom lenses, Silicon, Imaging systems, Optical design, Mid-IR, Modulation transfer functions, Lenses, Sensors, Diffraction
In this paper, a two-stage compact zoom MWIR continuous zoom scheme without rear fixed group is proposed. In this scheme, two zoom groups are used to achieve two step of zooming, and one compensation group is used for zoom compensation. Therefore, the mathematical model is deduced. The number of lenses can be reduced without rear-fixed group, and the problem of aberration correction can be compensated by introducing diffraction surface into the compensation group. A 15.3× medium-wave infrared continuous zoom optical system is designed by this method, which can match the medium-wave 640×512 and the pixel size of 15μm cooled focal plane array detector. The operating band of the continuous zoom system is 3.7~4.8μm, the F number is 5.5, the continuous zoom range is 18~275mm, and the total length of the optical system is only 108mm. The design results give the light path structure of the three position points of the Long focal, medium focal and short focal point, then analyze the modulation transfer function, spot diagram and narcissus, then optimize the design of CAM data, also the curve of zoom CAM and the feasible method of machining diffraction plane on silicon lens surface are given. The design results show that within 0.707 field of view, the MTF value of the system is greater than 0.13 at 30lp/mm in the whole continuous zoom range. The system is compact and has only 5 lenses. It has the advantages of large zoom ratio, lightness, miniaturization, excellent imaging quality and smooth zoom CAM curve. It can be widely used in forest fire prevention, maritime patrol and early warning, photoelectric tracking and aiming, monitoring and other fields.
