Optical system design of endoscope for artillery gun bore inspection

Due to its advantages of long working length, small aperture, and good rigidity, the endoscope can be employed for the defect detection within the inner walls of small-caliber artillery tubes, thereby achieving the purpose for inspecting and evaluating the quality of the internal chamber. This paper presents the design of a side-viewing dual-optical-path large-depth-of-field endoscope optical system tailored for small-caliber artillery ranging form Ф30 mm to Ф85 mm. By incorporating a shared right-angle prism, the final design achieves a full field of view (FOV) of 68° for the single-optical-path endoscope optical system, with a working distance of 1 099 mm, enabling effective imaging within a depth of field ranging from 12 mm to 40 mm. The effective aperture for light transmission is less than 4.5 mm, exhibiting a maximum field curvature of −0.37 mm and a maximum distortion value of −14.6%. The optical transfer function across the full FOV exceeds 0.2 at a spatial frequency of 45 lp/mm for all configurations, approaching the diffraction limit. The observation range of the dual-optical-path endoscope optical system meets the requirements for parallax generation. The design results demonstrate that this endoscope optical system possesses superior imaging quality, fulfilling the needs for three-dimensional measurement of defects within artillery chambers.