內窺鏡是用來觀察人體內部體腔的，通過它能直接觀察到內腔器官的組成形態。現在內窺鏡已成為醫療診斷和微創手術必不可缺的可靠工具。
Endoscope is used to observe the internal body cavity of human body. Through it, the composition and morphology of internal organs can be directly observed. Now endoscope has become an indispensable and reliable tool for medical diagnosis and minimally invasive surgery.
硬管內窺鏡雖然品種繁多,但基本結構是一致的,內部的光學系統是由一系列透鏡組成，其作用是把觀察到的物體通過光學系統成像在觀察者的視網膜上。
Although there are many kinds of rigid tube endoscopes, the basic structure is consistent. The internal optical system is composed of a series of lenses, which is used to image the observed objects on the observer's retina through the optical system.
硬管內窺鏡的光學系統通常由物鏡(含棱鏡)、棒鏡、目鏡三部分組成。
The optical system of rigid tube endoscope is usually composed of objective lens (including prism), rod lens and eyepiece.

物鏡系統：
Objective lens system:
物鏡通常是由2～4片鏡片（膠合鏡片）組合而成。物鏡的主要作用是把物體成像到鏡頭前。如果視向角不是0°(直視式)的話，如斜視、側視式內窺鏡，需要在物鏡組內放置轉像的棱鏡。
The objective lens is usually composed of 2 ~ 4 lenses (glued lenses). The main function of objective lens is to image the object in front of the lens. If the viewing angle is not 0 ° (direct viewing type), such as strabismus and side looking endoscope, the image conversion prism needs to be placed in the objective lens group.
由多組同樣尺寸的轉像透鏡組成。棒鏡的主要作用是把物鏡上成的像傳輸到光闌位置。根據內窺鏡的工作長度不同,棒鏡有1、3、5、7組轉像透鏡組成，通常轉像系統棒鏡的數量為奇數。
It is composed of multiple sets of image conversion lenses of the same size. The main function of the rod lens is to transmit the image formed on the objective lens to the position of the diaphragm. According to the working length of the endoscope, the rod mirror is composed of 1, 3, 5 and 7 groups of image conversion lenses. Generally, the number of rod mirrors in the image conversion system is odd.
目鏡系統：
Eyepiece system:
目鏡位于內窺鏡后方鏡體內。目鏡的主要作用是把光闌位置成的像放大，目鏡的放大倍數一般在15～30之間。放大倍數不能過大，否則物像將無法看清。<在硬管內窺鏡插入管部分，又外管、內管和照明光纖組成。照明光纖位于內管和外管之間，作用是照亮整個視場范圍。
The eyepiece is located in the body behind the endoscope. The main function of the eyepiece is to enlarge the image formed by the diaphragm. The magnification of the eyepiece is generally between 15 and 30. The magnification should not be too large, otherwise the object image will not be able to see clearly< The hard tube endoscope is inserted into the tube part, which is composed of an outer tube, an inner tube and a lighting optical fiber. The lighting fiber is located between the inner tube and the outer tube, and its function is to illuminate the whole field of view.