The lens is made according to the law of light refraction. It is an optical element made of transparent materials (such as glass, crystal, etc.). The lens is a refracting lens, and its refractive surface is a transparent body with two spherical surfaces (part of the spherical surface), or one spherical surface (part of the spherical surface) and one plane. The image formed by the lens has a real image and a virtual image. Lenses can be widely used in various fields such as security, automotive, digital cameras, lasers, optical instruments, etc. With the continuous development of the market, lens technology has become more and more widely used.

If the two interfaces of a transparent object are spherical, or one interface is spherical and the other interface is flat, then the object is called a lens. Lenses whose central part is thicker than the edges are called convex lenses. From their cross-sectional shape, there are three types: biconvex, plano-convex, and concave-convex. The lens whose central part is thinner than the edge is called concave lens. Different from its cross-sectional shape, it can be divided into three types: double-concave, plano-concave and convex-concave.

When the distance between the object and the convex lens is greater than 2 times the focal length, it becomes an inverted, reduced real image; when the distance between the object and the convex lens is between 2 times the focal length and the focal length, it becomes an inverted, enlarged real image; when the distance from the object to the convex lens is less than the focal length, it becomes a positive Vertical and enlarged virtual image.

As early as the Western Han Dynasty in China (206 BC to 25 AD, Huainan Wanbi Shu" has a record of ice lens: "Cut the ice to make a circle, lift it to the sun, and use Ai to bear its shadow, and then make a fire." That is us. Today, I’m talking about ice-cutting and making fire. It’s said that in the era of the Nile Mesopotamian civilization, priests were able to "catch fire from the sky" during religious ceremonies. The props used by the priests were a simple convex lens, which used the convex lens to converge the light. Function This feature ignites flammable materials. Two magnifying glasses are stored in the Egyptian Pavilion of the British Museum, which were discovered in Tanis, and the date is determined to be 150 AD.

It can be seen that since ancient times, people have known that the lens has the function of focusing and magnifying. Alhazen (965～1038) studied spherical mirrors and parabolic mirrors, first invented the convex lens and described the structure of the human eye.

In 1266, Bacon (R. Bacon, 1214 ~ 1294) first proposed the possibility of using lenses to correct vision and using lens groups to form a telescope, and described the position of the focal point of the lens.

1299 Florentine Armati invented glasses to solve the problem of vision correction.

1609 Galileo (GalileoGaliei, 1564～1642) exhibited the first telescope built in accordance with scientific theories in human history. In fact, Galileo was not the first to discover the mystery of the telescope, but a Dutch businessman named Lippershey (1587-1619). When he made the lens, he combined a convex lens with a concave lens and looked out, the distant scenery became closer. Galileo was very interested in this discovery. He used mathematical calculations to study what kind of lenses are better to combine. After repeated experiments, he finally invented the world's first telescope with a magnification of 32 times in 1909. He used the telescope he invented for astronomical observations and made many significant discoveries.

The first microscope was invented by the Dutchman Janssen (1588-1632). Later, the Italian Fontana (Fontana, 1580 ~ 1656) made significant improvements to this, changing the microscope eyepiece from a concave lens to a convex lens, so that it has the basic form of a modern microscope.

Currently, lenses have been used in the objective lenses of electron microscopes, projectors, cameras, etc. The development of the lens has gone through a long process, and its role has been brought into full play in all fields.