Abstract: In order to meet the needs of large angle coverage and high information acquisition, a long working distance wide-angle industrial endoscope with visible light range is designed. The basic structure of the lens is multistage imaging, where the objective lens system adopts the reverse telephoto structure, and the transformation image system adopts the lens type. The image surface of the lens is connected with a 1/3 inch CCD. Based on the comprehensive consideration of cost and image quality, the spherical transmissible and unglued scheme is finally adopted. The optimization design is carried out with ZEMAX software and the image quality is evaluated. Considering the cost and image quality, the spherical transmissive and unglued scheme is finally adopted. The final lens is composed of a sapphire window, 12 spherical lenses and a thick plane used to extend the optical path. The full field angle of the lens is 102◦, a focal length is 3.25 mm and the total working length is 730 mm. The diameter of the optical system’s entrance pupil is 1 mm, the radius of the imaging dispersion spot is within 6 µm, which is close to the diffraction limit. The modulation transfer function value at 50 lp/mm is greater than 0.4, and the maximum distortion value is less than 25%. The evaluation and analysis show that the design results meet the technical requirements and the structure is reasonable.

Key words: geometric optics, wide-angle industrial endoscope, multistage imaging, short focal length