The hard tube endoscope is mainly composed of an optical imaging system and an illumination system: the optical part looks like a slender metal tube, and inside is a complete optical system composed of many lenses. The optical imaging system consists of three major systems: the objective lens system, the image relay system, and the eyepiece system. The inverted image of the object to be observed is formed by the objective lens, and the inverted image is converted into a positive image by the relay system, and transmitted to the eyepiece, and then magnified by the eyepiece, and then observed by the human eye. As shown in Figure 1. In order to form different viewing angles, different prisms need to be added. Endoscopes for different purposes are made into different shapes, outer diameters and lengths according to the requirements of use to meet the requirements of use. The illumination transmission system is composed of optical fiber, which transmits the light of the cold light source to the front end of the endoscope through the optical fiber to illuminate the observed object.