To obtain a number of advantages in fabrication, testing and alignment, many designs in which spherical mirrors
replace classical Cassegrain-form aspheric mirrors are present in the literature. However, spherical mirrors suffer from
substantial spherical aberration and thereby require some form of corrector group. But in this case, the question
encountered is that of making the basic optical configuration more complex. In this paper, a new design based on Cooke
corrector group is presented for eliminating spherical aberration, which is believed to provide higher performance with
less complexity than previous approaches. Besides, the cost and fabrication period will be extremely decreased. The
telescope system using corrector group here can achieve good optical performance with f# of 10, full field of 0.5°,
obscuration of 1/3 and MTF (Modulation Transfer Function) of 0.48 corresponding to 50@lp/mm.