Lens definitions and example sentences on Wordnik

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Definitions (77)

American Heritage Dictionary (5)

noun A ground or molded piece of glass, plastic, or other transparent material with opposite surfaces either or both of which are curved, by means of which light rays are refracted so that they converge or diverge to form an image.
noun A combination of two or more such pieces, sometimes with other optical devices such as prisms, used to form an image for viewing or photographing. Also called compound lens.
noun A device that causes radiation other than light to converge or diverge by an action analogous to that of an optical lens.

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Century Dictionary (66)

A piece of transparent substance bounded by two curved surfaces (usually spherical), or by a curved surface and a plane. The ordinary use of a lens is to cause pencils of rays to converge or diverge systematically after passing through it. Lenses for optical purposes are usually made of glass; acoustic lenses, of carbon dioxid inclosed between two thin membranes; lenses for action upon electrical radiations, of paraffin or pitch, substances which are transparent to electrical rays, though opaque to light. Optical lenses alone are in common use. Ordinary lenses are distinguished into two classes—convex or magnifying lenses, which are thickest in the center, and concave, which are thinnest in the center. Each class has three varieties, as shown in fig. 1. To the first belong D, the double-convex or biconvex; C, the plano-convex; and E, the meniscus. The concave lenses are B, the double-concave or biconcave; A, the plano-concave; and F, the concavo-convex, sometimes improperly called concave meniscus. The line which passes through the centers of curvature of the two surfaces is the axis of the lens, and a point on this axis so taken that every line drawn through it pierces parallel elements of the two surfaces is its optical center. A convex lens converges rays which are parallel to its axis, approximately to a point called its principal focus (F in fig. 2). The distance from the optical center to this focus is the same on both sides of the lens, and depends upon the radii of its curved surfaces and the material of which it is made. Rays diverging from a point beyond the principal focus F on either side of the lens are approximately collected to a “real” focus beyond the principal focus on the other side (see fig. 3); but if the source of light is between the lens and its principal focus, the rays after emergence diverge as if they came from a so-called virtual focus behind the luminous point. The luminous point and its focus are interchangeable, and are called conjugate foci, as, for instance, L. and 1 in fig. 3. (See focus, 1.) A concave lens always renders still more divergent rays emanating from a point, and so forms only virtual foci. If the source of light is an extended surface, then the pencil of rays emanating from each point forms its own focus; and the collection of foci constitutes an image, which is real and inverted if the foci are real, but virtual and erect if they are virtual. The relative sizes of the object and image are sensibly proportional, if the lens is thin, to their respective distances from the optical center; if the lens is thick, the distances must be reckoned from the two so-called principal points of the lens (see principal point, under point), which lie on the axis on each side of the optical center. An image formed by a single lens is never perfectly distinct, on account of the spherical and chromatic aberrations of the lens. (See aberration, 4.) The former is due to the fact that a lens bounded by spherical surfaces converges marginal rays to a point nearer the lens than that in which the central rays meet; the latter, to the fact that rays of different color form thoir foci at different distances, the focal distance for violet rays being (with a glass lens) nearly a seventh part shorter than that for the red rays. The spherical aberration can be corrected by making the surfaces of forms other than spherical, or by combining two or more lenses properly proportioned; the chromatic aberration, only by combining two or more convex and concave lenses of different materials, usually a convex of crown-glass with a concave of flint-glass.
In anatomy, in the eye, a double-convex body placed in the axis of vision behind the iris between the aqueous humor and the vitreous humor, serving to focus rays of light upon the retina; the crystalline lens. See first cut under eye.
Figuratively, photography, from the use of lenses in that art. So thoroughly has this region been set forth by the pen and the pencil and the lens that I am relieved of the necessity of describing it. Harper's Mag., LXXVIII. 258.

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This lens is also designed for movie recording use by minimizing the mechanical sound generated by the continuous AF / AE action. — News: Digital Photography Review (dpreview.com)
Overall, this lens is an excellent all-around performer. — DigitalCameraReview.com Digital Camera News and Reviews
Though the lens is an important functional part of the Vado, it is by no means the most noticeable feature on the front of the camcorder. — CamcorderInfo.com News & Reviews
Anyways, the lens was already preset to f2. 8 before I put the extension tubes. — winterheim|hdd
First, if you accidentally press the lens-release button even slightly, a black screen comes up saying, "Please check that the lens is attached correctly." — Imaging Resource News Page

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lens

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