Search the Dictionary

light meet, after being reflected or refrcted, and at which the image is formed; as, the focus of a lens or mirror.

light emanating from one and the same point, or the deviation of such rays from a single focus; called spherical aberration, when due to the spherical form of the lens or mirror, such form giving different foci for central and marginal rays; and chromatic aberration, when due to different refrangibilities of the color…

Uniting the chemical rays of light into one focus, as a certain kind of lens; amacratic.

t curvatures, so combined as to remove spherical aberration; -- said of a lens. Aplanatic focus of a lens (Opt.), the point or focus from which rays diverging pass the lens without spherical aberration. In certain forms of lenses there are two such foci; and it is by taking advantage of this fact that the best aplanati…

ion; -- said esp. of a lens in which rays of three or more colors are brought to the same focus, the degree of achromatism thus obtained being more complete than where two rays only are thus focused, as in the ordinary achromatic objective. --Ap`o*chro"ma*tism (#), n.

f considerable size, used for producing an intense heat by converging the sun's rays to a focus. -- Burning house (Metal.), the furnace in which tin ores are calcined, to sublime the sulphur and arsenic from the pyrites. Weale. -- Burning mirror, a concave mirror, or a combination of plane mirrors, used for the same…

nvex lens or a concave mirror, are thrown on a paper or other white surface placed in the focus of the lens or mirror within a darkened chamber, or box, so that the oulines may be traced.

ugh the optical center of the object glass and the intersection of the cross wires at its focus.

convex lens at one end and at the other a small opening or slit which is at the principal focus of the lens, used for producing a beam of parallel rays; also, a lens so used.

To draw or direct to a common center; to bring together at a focus or point, as two or more lines; to concentrate. In thee concentering all their precious beams. Milton. All is concentered in a life intense. Byren.

to gather into one body, mass, or force; to fix; as, to concentrate rays of light into a focus; to concentrate the attention. (He) concentrated whole force at his own camp. Motley.

or hyperbola such that each bisects all chords drawn parallel to the other. -- Conjugate focus (Opt.) See under Focus. -- Conjugate mirrors (Optics), two mirrors so placed that rays from the focus of one are received at the focus of the other, especially two concave mirrors so placed that rays proceeding from the pri…

to one point; to cause to incline and approach nearer together. I converge its rays to a focus of dazzling brilliancy. Tyndall.

tending to one point of focus; tending to approach each other; converging. As many rays of light, as conveniently can be let in, and made convergent. Boyle. The vast dome of its cathedral . . . directing its convergent curves to heaven. Hallam.

To converge to one point or focus, as light or rays.

y bodies. -- Crystalline lens (Anat.), the capsular lenslike body in the eye, serving to focus the rays of light. It consists of rodlike cells derived from the external embryonic epithelium.

circular, used in instruments to cut off marginal portions of a beam of light, as at the focus of a telescope.

oint of the curve from it has a constant ratio to the distance of the same point from the focus.

The ratio of the distance between the center and the focus of an ellipse or hyperbola to its semi-transverse axis.

r axis, and the least diameter is the minor axis. See Conic section, under Conic, and cf. Focus.