A lens with a focal length of 5 mm is also called a standard lens, because its viewing angle of about 39 degrees on the Quan Huafu is equivalent to that of human eyes. It is said that the lens is the photographer's third eye, and the world seen through a 5 mm lens can truly restore the atmosphere at that time; A wide-angle lens is, in short, a lens with a short focal length, a wide viewing angle and a deep depth of field. The basic characteristics of a wide-angle lens are that the lens has a large viewing angle and a wide field of vision, and the range of scenery observed from a certain viewpoint is much larger than that seen by human eyes at the same viewpoint, and the depth of field is long; The telephoto lens can ignore the redundant picture and highlight the main body. The telephoto lens has a relatively narrow viewing angle, and can focus on the subject or portrait, so it can avoid unnecessary factors and make the subject of the photo more concentrated.