Fig. 1. Schematic of industrial rigid endoscopic system

Fig. 2. Optical system structure of objective lens in visible band

Fig. 3. Schematic of Hopkins triple glued rod lens system

Fig. 4. Single-group rod lens optical system structure in visible wavelength band

Fig. 5. Optical system structure of visible wavelength endoscopes

Fig. 6. MTF curves of visible waveband optical system

Fig. 7. Spot diagram of visible waveband optical system

Fig. 8. Optical system structure of infrared dual-band objective lens

Fig. 9. Single-group rod lens optical system structure in infrared wavelength band

Fig. 10. Optical system structure of infrared dual-band endoscope

Fig. 11. MTF curves of infrared optical system

Fig. 12. Spot diagram of infrared optical system

Fig. 13. MTF curves of visible optical system at different temperatures

Fig. 14. MTF curves of mid-wave infrared optical system at different temperatures

Fig. 15. MTF curves of long-wave infrared optical system at different temperatures

Fig. 16. Tolerance analysis results

Fig. 17. Physical image of dual-channel industrial endoscope

Fig. 18. Visible-band endoscopic resolution experiment

Fig. 19. Endoscopic imaging effects at different distances

Fig. 20. Experimental diagram of endoscope in furnace chamber