ETYM Latin lens a lentil. So named from the resemblance in shape of a double convex lens to the seed of a lentil. Related to Lentil.
(Irregular plural: lenses).
1. A transparent optical device used to converge or diverge transmitted light and to form images; SYN. lens system.
2. Biconvex transparent body situated behind the iris in the eye; it focuses light waves on the retina; SYN. crystalline lens.
3. Equipment that uses a magnetic or electric field in order to focus a beam of electrons; SYN. electron lens.
A transparent object with two refracting surfaces. Usually the surfaces are flat or spherical (spherical lenses). Sometimes, to improve image quality. Lenses are deliberately made with surfaces which depart slightly from spherical (aspheric lenses).
In optics, a piece of a transparent material, such as glass, with two polished surfaces—one concave or convex, and the other plane, concave, or convex—that modifies rays of light. A convex lens brings rays of light together; a concave lens makes the rays diverge. Lenses are essential to glasses, microscopes, telescopes, cameras, and almost all optical instruments.
The image formed by a single lens suffers from several defects or aberrations, notably spherical aberration in which a straight line becomes a curved image, and chromatic aberration in which an image in white light tends to have colored edges. Aberrations are corrected by the use of compound lenses, which are built up from two or more lenses of different refractive index.
Coal-mining town in Pas-de-Calais département, France; conurbation 327,000. During World War I it was in German occupation and close to the front line Oct 1914–Oct 1918, when the town and its mines were so severely damaged that mining operations could not re-start until 1921. In World War II it was occupied by Germany, May 1940–Sept 1944, but suffered less physical damage.