Fig. 1. Mathematical model for OPD of single-mirror reflective optical system

Fig. 2. Relation diagram of ray incidence angle with tangent slope (K) and normal slope (S)

Fig. 3. Schematic diagram of microelement segmentation method

Fig. 4. Mathematical model for WE of single-mirror reflective optical system

Fig. 5. Flow chart of desensitization optimization design for large freeform off-axis three-mirror optical systems

Fig. 6. Light sampling diagram. (a) FOV sampling diagram; (b) Pupil sampling diagram

Fig. 7. Initial system obtained after image quality optimization-System 1: (a) System layout, (b) MTF diagram, (c) RMS WFE diagram of full FOV

Fig. 8. Optical system optimized by angle optimization desensitization design method-System 2, optical system optimized by local curvature control desensitization design method-System 3. Optical system layout: (a) System 2, (b) System 3; MTF diagram: (c) System 2, (d) System 3; RMS WFE diagram of full FOV: (e) System 2, (f) System 3

Fig. 9. (a) RMS WFE comparison diagram after tilt misalignment and (b) ΔRMS WFE comparison diagram of System 1, System 2 and System 3