The lens is the basic optical element of the optical system of a microscope. The objective lens, eyepiece and condenser lens are all composed of single or multiple lenses. According to its shape, can be divided into convex lens also called positive lens and concave lens also called negative lens two categories.

Convex lens: thick in the middle, thin edge, double convex, flat convex, concave-convex three;

Concave lens: thin in the middle, thick edge, double concave, flat concave, convex concave three.

When a beam of light passing through a convex lens parallel to the main beam is compared to a point, that point is called the focal point, and the plane passing through the focal point perpendicular to the axis of light is called the focal plane. There are two focal points. At the focal point of the object space, it is called the "object focal point", and the focal plane of the object is called the object focal plane. On the contrary, at the focal point of the image space, it is called the image focal point, and the focal plane of the object is called the image focal plane.

When the light passes through a concave lens, it becomes an upright virtual image, while the side of a convex lens becomes an inverted real image. The real image can be displayed on the screen, while the virtual image cannot.

Lens can be widely used in security, vehicle, digital camera, laser, optical instruments and other categories, with the development of the market from time to time, lens technology is more and more widely used. A lens is made according to the law of refraction of light. A lens is an optical element made of a transparent substance, such as glass, crystal, etc. A lens is a refractor whose refracting surface is a transparent body of two spheres (a part of a sphere) or a sphere (a part of a sphere) and a plane. The images it makes are both real and virtual.