A lens is an optical component made of transparent materials such as glass, crystal, etc. A lens is a refractive mirror, whose refractive surface is a transparent body consisting of two spherical surfaces (part of the spherical surface) or one spherical surface (part of the spherical surface) and one plane. It forms both real and virtual images. Lenses can generally be divided into two categories: convex lenses and concave lenses. A lens with a central portion thicker than the edge portion is called a convex lens, which has three types: biconvex, plano convex, and concave convex; A concave lens with a thinner central part than the edge part is called a concave lens, which can be divided into three types: double concave, flat concave, and convex concave.