In order to find unvignetted target in the large field of regard in gimbaled conformal seeker, a freeform corrector and slight zoomed catadioptric real imaging system are used to balance and correct dynamic aberrations. The RMS spot diameter of the slight zoomed conformal optical system is near or smaller than the pixel size in all field of regard. Besides, the system achieves near diffraction limited performance even in big field of regard.