Fig. 1. Characterizations and definitions for local focal length

Fig. 2. Characterization and calculations for local entrance pupil. (a) Local entrance pupil for fisheye lens; (b) Local entrance pupil for off-axis three-mirror camera; (c) Local entrance pupil calculations based on ray tracing

Fig. 3. The optical layout of 120° wide angle lens of case 1 with the combination of rectilinear projection and equidistant projection

Fig. 4. Imaging performance of the 120° wide angle lens of case 1. (a) MTF curves; (b) Spot diagrams for different FOV; (c) Relative illumination curves

Fig. 5. Mapping relationship of the 120° wide angle lens of case 1. (a) LFL curves varying with FOVs; (b) LFL relative error and image height relative curves varying with FOVs; (c) Grid distortions

Fig. 6. The optical layout of 120° wide angle lens with uniform IFOV within two FOVs. (a) Case 2; (b) Case 3

Fig. 7. Imaging performance of the 120° wide angle lens of case 2 and case 3. (a) MTF curves of case 2; (b) Spot diagrams for different FOV of case 2; (c) Relative illumination curves of case 2; (d) MTF curves of case 3; (e) Spot diagrams for different FOV of case 3; (f) Relative illumination curves of case 3

Fig. 8. The LFL curves varying with FOVs for 120° wide angle lens with uniform IFOV within two FOVs. (a) Case 2; (b) Case 3

Fig. 9. The IFOV curves varying with FOVs for three cases of 120° wide angle lens