Fig. 1. Equivalent aperture offset vector in the pupil off-axis freeform system

Fig. 2. Astigmatism FFDs of the pupil off-axis system. (a) Spherical system without spherical aberration; (b) freeform surface system with Z5/6

Fig. 3. Distribution of pupil off-axis freeform system with Z7/8. (a) Position of the symmetrical center of two nodes; (b) FFDs of astigmatism

Fig. 4. FFDs of coma. (a) Pupil off-axis spherical system; (b) pupil off-axis freeform system with Z7/8

Fig. 5. Two nodes distribution of pupil off-axis freeform system with Z9. (a) q<0; (b) q>0

Fig. 6. FFDs of coma. (a) Pupil off-axis spherical system; (b) pupil off-axis freeform system with Z9

Fig. 7. Effect of different residual aberrations on PSF ellipticity. (a) Residual spherical aberration; (b) residual coma after correcting astigmatism; (c) residual astigmatism after correcting coma; (d) residual coma and astigmatism

Fig. 8. Initial configuration of the pupil off-axis optical system

Fig. 9. (a) FFDs of astigmatism distribution of the conic system; (b) PSF ellipticity of the full field

Fig. 10. Effect of different Zernike coefficients on PSF ellipticity

Fig. 11. Layout of the optimized system

Fig. 12. (a) Third-order astigmatism FFDs of the optimized system; (b) third-order coma FFDs of the optimized system

Fig. 13. (a) Full field PSF ellipticity of the optimized system; (b) RMS value of the wavefront error

Fig. 14. MTF curves of the optimized system