1. The threemirror anastigmatic system includes two aspherical concave mirrors and a spherical convex mirror.

2. Anastigmatic lens : Photographic lens corrected astigmatism as well as other distortions. Process camera lenses are anastigmats.

3. Anastigmatic mounts of concave gratings based on this algorithm are optimized, and numerical results are simulated.

4. Results There were 31 cases of anastigmatic recurrence, the signs on CT were mass around anastigmatic.

5. Anastigmatic lens : Photographic lens corrected for astigmatism as well as other distortions.

6. It is also shown that only when the gratings are cylinder or plane ones, the second order sagittal anastigmatic circular field and meridional non defocus flat field spectral images can be formed.