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focus

(Encyclopedia)focus, in optics, the point at which rays converge after reflection by a concave mirror or refraction by a convex lens, also known as a real focus. The point from which rays appear to diverge after re...

microscope

(Encyclopedia)CE5 Compound microscope microscope, optical instrument used to increase the apparent size of an object. The electron microscope, which is not limited by the powers of optical lenses and light,...

Clark, Alvan

(Encyclopedia)Clark, Alvan, 1804–87, American astronomer and maker of astronomical lenses, b. Ashfield, Mass. In 1846 the firm of Alvan Clark & Sons was established at Cambridgeport, Mass.; it became famous a...

camera

(Encyclopedia)CE5 Image formed by a camera camera, lightproof box or container, usually fitted with a lens, which gathers incoming light and concentrates it so that it can be directed toward the film (in an opt...

farsightedness

(Encyclopedia)farsightedness or hyperopia, condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the r...

optics

(Encyclopedia)optics, scientific study of light. Physical optics is concerned with the genesis, nature, and properties of light; physiological optics with the part light plays in vision; and geometrical optics with...

binocular

(Encyclopedia)CE5 Binocular binocular, small optical instrument consisting of two similar telescopes mounted on a single frame so that separate images enter each of the viewer's eyes. As with a single telescope...

lentil

(Encyclopedia)lentil, leguminous Old World annual plant (Lens culinaris) with whitish or pale blue flowers. Its pods contain two greenish-brown or dark-colored seeds, also called lentils, which when fully ripe are ...

O'Brien, Fitz-James

(Encyclopedia)O'Brien, Fitz-James, 1828?–1862, Irish-American author and journalist, b. Ireland. He settled in New York in 1852. He is remembered for two of his short stories, “The Diamond Lens” and “The Wo...

eye

(Encyclopedia)CE5 Cross section of human eye eye, organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of ey...