含有阶梯微反射镜和片状分束器的时空联合调制型傅里叶变换成像光谱仪的前置成像系统不仅要满足与阶梯微反射镜参数相匹配，还需具有实入瞳和像方远心的特性。为此，研究了将普通红外物镜转变为具有实入瞳的像方远心结构的方法。同时，研究了片状分束器和补偿板所带来的离轴像差，并提出了采用柱面和泽尼克面相结合的矫正方法以提高成像质量。设计出满足光谱范围3~5 μm、F 数为4、有效焦距为400 mm、视场为4.58°的整个波段全视场范围内无渐晕的红外光学系统。仿真结果表明：前置成像系统的成像质量接近衍射极限，最大全视场均方根光斑直径为5.9 μm。这种设计方法可以用于大孔径时空联合调制型傅里叶变换成像光谱仪前置成像系统设计。

Containing stepped micro- mirror and flaky beam splitter, prefixing objective of spatio- temporally modulated Fourier transform imaging spectrometer is not only to match with parameters of ladder micromirror,but also to have telecentric characteristic with a real entrance pupil. To this end, this paper studies a method to transform the ordinary infrared lens into a telecentric construction with a real entrance pupil.Meanwhile, the study of off axis aberrations caused by the sheet beam splitter and compensation plate proposes a correction method applying a combination of cylindrical and Zernike surface to improve image quality. Based on the method, with the specific requirements of 3~5 mm spectral range, F number of 4, 400 mm effective focal length, no vignetting within full field of view of 4.58° , an infrared optical system is designed.Simulation results show that: the image quality of front objective is closed to the diffraction limit with the maximum root mean square (RMS) spot diameter 5.9 mm in full field, and the distortion less than 0.3% . So this method can be used for the design of the front lens with large aperture in spatio-temporally modulated Fourier transform imaging spectrometer.