LENS

    Lens, a piece of transparent material with one or more surfaces curved so as to form an optical image. Ordinary lenses are used with visible light, but for special purposes they may be used with ultraviolet or infrared light. They are commonly made of glass, but plastics often and crystal occasionally may serve as lens materials. The human eye has a lens made of elastic material confined between transport transparent membranes, and its focus is adjusted by stretching of the fibrous material of the lens.

    The action of an optical lens is simulated in the focusing of electromagnetic radiation other than light or of streams of particles. Thus an array of materials constructed so as to focus microwaves may be referred to as a lens, and an electric or magnetic field used to focus a stream of electrons as in a television tube is referred to as an electron lens.

    Lenses have a multitude of important applications in science, industry, and everyday life, ranging from the giant telescopes that explore the heavens to the eyeglasses that many people must wear to correct for vision deficiencies.

light dispersion caused by a kind of lens, a prism