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Key People:Giuseppe CampaniJohn Henry DallmeyerAlvan Graham Clark...(Show more)Related Topics:SpeedFresnel lensApertureFocal lengthDrum lens...(Show more)
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lens, in optics, item of glass or various other transparent substance the is used to form an picture of an item by focusing rays of light from the object. A lens is a item of transparent material, typically circular in shape, v two sleek surfaces, either or both of i beg your pardon is curved and may be either convex (bulging) or concave (depressed). The curves are nearly always spherical; i.e., the radius the curvature is constant. A lens has actually the an important property of forming images the objects located in front of it. Single lenses are used in eyeglasses, call lenses, bag magnifiers, projection condensers, signal lights, viewfinders, and on simple box cameras. An ext often a number of lenses make of different materials are merged together together a compound lens in a tube to allow the mediate of aberrations. Link lenses are provided in such tools as cameras, microscopes, and also telescopes.

Optical values for lenses

A lens produces its concentrating effect due to the fact that light travels more slowly in the lens 보다 in the neighboring air, so the refraction, one abrupt bending, the a irradiate beam wake up both where the beam start the lens and where it increase from the lens right into the air.


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(Left) overcome sections that standard develops of common lenses. (Right) Refraction of light by converging and also diverging lenses, reflecting the primary axis, the principal emphasis (or focal length point) F, the focal length f, and also the focal distance plane.

A single lens has actually two precisely constant opposite surfaces; one of two people both surfaces are curved or one is curved and one is plane. Lenses might be classified follow to their 2 surfaces as biconvex, plano-convex, concavo-convex (converging meniscus), biconcave, plano-concave, and also convexo-concave (diverging meniscus). Because of the curvature of the lens surfaces, various rays the an incident light beam space refracted through different angles, so that whole beam the parallel rays have the right to be led to to converge on, or to show up to diverge from, a solitary point. This point is called the focal length point, or principal focus, of the lens (often depicted in ray diagrams together F). Refraction that the beam of irradiate reflected native or emitted by an item causes the beam to form a visual picture of the object. This photo may be either real—photographable or visible on a screen—or virtual—visible only upon looking right into the lens, as in a microscope. The picture may it is in much bigger or smaller sized than the object, depending on the focal size of the lens and also on the distance between the lens and the object. The focal length of a lens is the street from the centre of the lens come the allude at i beg your pardon the image of a remote object is formed. A long-focus lens forms a larger image of a distant object, if a short-focus lens forms a tiny image.

Usually the image developed by a solitary lens is not good enough for specific work in such fields as astronomy, microscopy, and also photography; this is since the cone of light ray emitted by a single point in a far-off object is not unified in a perfect point by the lens but instead forms a tiny patch of light. This and other inherent imperfections in a lens’s photo of a single object suggest are known as aberrations. To correct together aberrations, it is often important to combine in one mount number of lens facets (single lenses), several of which may be convex and some concave, part made of thick high-refractive or high-dispersive glass, and others made of low-refractive or low-dispersive glass. The lens facets may it is in cemented together or an installed at closely calculated separations to exactly the aberrations of the separation, personal, instance elements and obtain photo of agree sharpness (see also aberration). The an accurate mounting additionally ensures the all lenses are effectively centred; the is, the centres of curvature of all the lens surface lie top top a single straight line dubbed the principal axis of the lens. A generally used measure of the quality of any kind of lens system is its capacity to form an photo that is sharp sufficient to separate, or resolve, two an extremely close dots or currently in one object. Resolving power depends on just how well the assorted aberrations in a lens system are corrected.

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The most basic compound lens is a slim cemented combination of two solitary lenses, such as that offered in the target (the lens nearest the object) that a little refracting telescope. Microscope objectives might contain as countless as eight or nine elements, few of which might be do of various materials in bespeak to bring all color of irradiate to a typical focus, and thus stop chromatic aberration. The target lenses used in cameras might contain from two to 10 elements, if a so-called zoom or variable-focal size lens may have as numerous as 18 or 20 facets in number of groups, the different groups being movable follow me the axis by levers or cams in order to develop the desired adjust in focal length without a shift of the focal length plane. Lenses likewise vary substantially in diameter, native as small as 0.16 cm (1/16 inch) for an facet in a microscopic lense objective come as big as 100 cm (40 inches) for an expensive telescope objective. In reflectors and also several other varieties of astronomical telescopes, concave mirrors are provided for the objective instead of lenses.