Fig. 1. Schematic diagram of endoscope structure

Fig. 2. Initial structure diagram of front objective lens

Fig. 3. Initial structure diagram of rear objective lens

Fig. 4. 2D diagram of optimized front objective lens group

Fig. 5. MTF curves of optimized front objective lens group

Fig. 6. Structure diagram of spliced system

Fig. 7. Spot diagram of system

Fig. 8. Mesh distortion diagram

Fig. 9. MTF curves

Fig. 10. Image simulation

Fig. 11. Curves of relative illumination

Fig. 12. MTF curves of system at initial high temperature

Fig. 13. MTF curves of system at three temperatures