It is the astigmatism that leads the traditional imaging spectrometer based on Czerny-Turner to have low spatial
resolution. And it is discovered that when the distance between concave mirror and grating, x, is equal to the twice of
focal length, , of the mirror, SII = SIII = 0 and the aberration is the least as well as the astigmatism is eliminated greatly.
Meanwhile the toroidal mirror is presented to correct the astigmatism, and as well the aberration caused by the large
FOV is corrected by optimizing the surface tilt. Then both of the spatial and spectral resolutions are improved. Finally a
Czerny-Turner imaging spectrometer working in FUV (120 nm ~ 180 nm) with 2.5° FOV is designed, and its focal
length is 147.61 mm, its F number is 3.93. MTF of this imaging spectrometer is more than 0.39 at 20 lp/mm in the total
wavelength band of FOV, which satisfied the requirements of imaging spectrometer working on satellite in FUV.