Fig. 1. Principle of Shack-Hartmann sensor^[4]. (a) Spots of flat wavefront; (b) spots of wavefront with aberration

Fig. 2. Diagram of testing process of single sub-aperture

Fig. 3. Mirror area covered by sub-apertures

Fig. 4. Structure of Cassegrain system

Fig. 5. Initial aberration of the system

Fig. 6. Variation of RMS relative error with the order of aberration

Fig. 7. Recovery effect comparison of different order aberrations. (a) Recovery wavefront of the 8^th-order aberration; (b) reference wavefront of the 8^th-order aberration; (c) recovery wavefront of the 29^th-order aberration; (d) reference wavefront of the 29^th-order aberration

Fig. 8. Detection effect of low-order aberrations. (a) Reference aberration; (b) recovery aberration

Fig. 9. Detection results while adding high-order aberrations. (a) Recovery wavefront; (b) reference wavefront; (c) low-order residual; (d) high-order residual

Fig. 10. Three distribution types of sub-aperture. (a) Sparse sub-aperture distribution; (b) tangent sub-aperture distribution; (c) intensive sub-aperture distribution

Fig. 11. Recovery effect comparison of different sub-aperture distribution types. (a) Reference aberration introduced by the Zernike surface type; (b) recovery wavefront of sparse sub-aperture distribution; (c) recovery wavefront of tangent sub-aperture distribution; (d) recovery wavefront of intensive sub-aperture distribution

Fig. 12. Detection error curves under different sub-aperture numbers. (a) RMS relative error; (b) PV relative error

Fig. 13. Fitting curve of detection error with the number of sub-apertures