Fig. 1. Design process of unobscured off-axis initial structure. (a) Spherical coaxial structure. (b)(c) process of eliminating obscuration by surface tilt deviation; (d) unobscured off-axis initial structure

Fig. 2. System for ideal point-to-point imaging in single field of view based on confocal quadric surface

Fig. 3. Structure of cylindrical package off-axis three-mirror system using confocal off-axis quadric surface

Fig. 4. Sketch of cylindrical package freeform off-axis three-mirror system in meridian plane

Fig. 5. Final system structure after optimization. (a) Two-dimensional plot of final system structure; (b) three-dimensional plot of final system structure

Fig. 6. Image quality of final system. (a) Field map of RMS wavefront error; (b) distortion grid; (c) field map of MTF in x direction at spatial frequency of 33 lp/mm; (d) field map of MTF in y direction at spatial frequency of 33 lp/mm

Fig. 7. Footprint plots of typical field points at virtual plane of M1 front object space

Fig. 8. Tolerance analysis result of 2000-round Monte Carlo analysis. (a) Cumulative probability curve of MTF at spatial frequency of 33 lp/mm in x direction; (b) cumulative probability curve of MTF at spatial frequency of 33 lp/mm in y direction