Mohist scholars Shen Kuo and Zhao Youqin have made the most outstanding achievements in the study of ancient optics in China. Their research achievements can be found in Mo Jing, Meng Qian Bi Tan, Cao Xiang Xin Zhu and so on. Mo Jing recorded the earliest pinhole imaging experiment in the world, and correctly analyzed and explained pinhole imaging. The Mohist Classic also records the viewpoint that the propagation of light is a straight line, and discusses the imaging of plane mirror, concave mirror and convex mirror. Mo Jing is the earliest work on geometric optics in the world.
Geometric optics is an important branch of optics, which studies the propagation and imaging law of light based on light. In geometric optics, the object points that make up an object are regarded as geometric points, and the beams emitted by them are regarded as a collection of countless geometric rays, and the direction of the rays represents the propagation direction of light energy. Under this assumption, it is very convenient and practical to study the imaging process of lens or other optical elements and design the optical system of optical instruments according to the propagation law of light.
Mo Jing is rich in knowledge of mechanics, optics, geometry, engineering technology and the basic elements of modern physics and mathematics. Among them, the balance and system of force, simple machinery such as lever and inclined plane are discussed, and the concepts of time ("long", that is, week) and space ("surplus") are put forward for the first time. It describes the linear propagation of light, which is a very important principle in modern optics and lays a certain foundation for the emergence and development of quantum communication. Joseph Needham, a famous sinologist in the West, once praised: "The scientific level of Mohism surpassed that of ancient Greece." It can be said that Mozi is "the ancestor of China scientists" and "a saint".