A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. Axial symmetry is Symmetry around an axis an object is axially symmetric if its appearance is unchanged if rotated around some axis In Optics and Spectroscopy, transmittance is the fraction of incident light at a specified Wavelength that passes through a sample Refraction is the change in direction of a Wave due to a change in its Speed. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 A simple lens is a lens consisting of a single optical element. In Optics, a simple lens or singlet lens is a lens consisting of a single simple element A compound lens is an array of simple lenses (elements) with a common axis; the use of multiple elements allows more optical aberrations to be corrected than is possible with a single element. Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. Manufactured lenses are typically made of glass or transparent plastic. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many In Optics, transparency (also called pellucidity) is the Material property of allowing Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Elements which refract electromagnetic radiation outside the visual spectrum are also called lenses: for instance, a microwave lens can be made from paraffin wax. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 In chemistry paraffin is the common name for the Alkane Hydrocarbons with the general formula C n H2 n +2

The archaic spelling lense is sometimes seen, but Merriam-Webster's medical dictionary is the only major dictionary that considers this to be correct. ^[1]

Contents 1 History 2 Construction of simple lenses 2.1 Types of simple lenses 2.2 Lensmaker's equation 2.2.1 Sign convention of lens radii R1 and R2 2.2.2 Thin lens equation 3 Imaging properties 4 Aberrations 4.1 Spherical aberration 4.2 Coma 4.3 Chromatic aberration 4.4 Other types of aberration 4.5 Aperture diffraction 5 Compound lenses 6 Uses of lenses 7 See also 8 References 8.1 General 8.2 Footnotes 9 External links

History

See also: History of optics

The oldest lens artefact is the Nimrud lens, which is over three thousand years old. Optics began with the development of lenses by the Ancient Egyptians and Mesopotamians followed by theories on Light and vision developed by ancient The Golden Gate Bridge is a suspension Bridge spanning the Golden Gate, the opening of the San Francisco Bay onto the Pacific Ocean Refraction is the change in direction of a Wave due to a change in its Speed. Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to A drop or droplet is a small volume of Liquid, bounded completely or almost completely by Free surfaces Surface tension The Nimrud lens is a 3000 year old piece of Rock crystal, which was unearthed by Austen Henry Layard at the palace of Nimrud in what is now Iraq ^[2] David Brewster proposed that it may have been used as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight. Sir David Brewster, FRS ( 11 December 1781 &ndash 10 February 1868) was a Scottish scientist inventor and writer magnifying glass (called a hand lens in laboratory contexts is a convex lens which is used to produce a magnified Image of an object A burning-glass is a large convex lens that can concentrate the Sun 's rays onto a small area heating up the area and thus resulting in ignition of the ^[2][3] Assyrian craftsmen made intricate engravings, and could have used such a lens in their work.

The earliest written records of lenses date to Ancient Greece, with Aristophanes' play The Clouds (424 BC) mentioning a burning-glass (a biconvex lens used to focus the sun's rays to produce fire). The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca Aristophanes (Ἀριστοφάνης ˌærɪˈstɒfəniːz in English ca The Clouds (Νεφέλαι / Nephelai) is a comedy written by the Ancient Greek playwright Aristophanes lampooning the Sophists In Geometrical optics, a focus, also called an image point, is the point where Light rays originating from a point on the object converge. The Sun (Sol is the Star at the center of the Solar System. The writings of Pliny the Elder (23–79) also show that burning-glasses were known to the Roman Empire,^[4] and mentions what is possibly the first use of a corrective lens: Nero was said to watch the gladiatorial games using an emerald^[5] (presumably concave to correct for myopia, though the reference is vague). Gaius or Caius Plinius Secundus, ( AD 23 – August 25, AD 79 better known as Pliny the Elder, was an ancient Author The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus Nero Claudius Caesar Augustus Germanicus ( December 15, 37 – June 9, 68) born Lucius Domitius Ahenobarbus, also called Gladiators (gladiatores "swordsmen" or "one who uses a sword" from la ''gladius'' "sword" were professional fighters in Ancient Rome who fought Emeralds are a variety of the Mineral Beryl (Be3Al2(SiO36 colored Green by trace amounts Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect Both Pliny and Seneca the Younger (3 BC–65) described the magnifying effect of a glass globe filled with water. Lucius Annaeus Seneca (often known simply as Seneca, or Seneca the Younger; Σένεκας in Ancient Greek literature (c Water is a common Chemical substance that is essential for the survival of all known forms of Life.

The word lens comes from the Latin name of the lentil, because a double-convex lens is lentil-shaped. The lentil or daal or pulse ( Lens culinaris) is a bushy Annual plant of the legume family grown for its lens-shaped Seeds The genus of the lentil plant is Lens, and the most commonly eaten species is Lens culinaris. The genus Lens of the Legume family Fabaceae contains four species of small erect or climbing Herbs with pinnate leaves and small inconspicuous The lentil plant also gives its name to a geometric figure. In Geometry, a lens is a Convex Shape comprising two circular arcs joined at their endpoints

The Arabian mathematician Ibn Sahl (c. This article is about the physicist For the physician see Ali ibn Sahl Rabban al-Tabari. 940–c. 1000) used what is now known as Snell's law to calculate the shape of lenses. In Optics and Physics, Snell's law (also known as Descartes' law or the law of refraction) is a formula used to describe the relationship ^[6] Ibn al-Haitham (965–1038) wrote the first major optical treatise, the Book of Optics, which described how the lens in the human eye formed an image on the retina. TemplateInfobox Muslim scholars --> ( Arabic: ابو علی، حسن بن حسن بن هيثم Latinized The Book of Optics ( Arabic: Kitab al-Manazir, Latin: De Aspectibus or Opticae Thesaurus Alhazeni The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain The vertebrate retina is a light sensitive part inside the inner layer of the Eye.

Excavations at the Viking harbour town of Fröjel, Gotland, Sweden discovered in 1999 the rock crystal Visby lenses, produced by turning on pole-lathes at Fröjel in the 11th to 12th century, with an imaging quality comparable to that of 1950s aspheric lenses. A Viking is one of the Norse ( Scandinavian Explorers Warriors Merchants, and pirates who raided and colonized wide areas is a county, province and municipality of Sweden and the largest Island in the Baltic Sea. "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. The Visby lenses are a collection of lens -shaped manufactured objects made of Rock crystal (quartz found in a Viking grave in Gotland dating The Viking lenses concentrate sunlight enough to ignite fires.

Widespread use of lenses did not occur until the use of reading stones in the 11th century and the invention of spectacles, probably in Italy in the 1280s. A reading stone was an approximately hemispherical transparent object placed on top of text to magnify the letters so that people with Presbyopia could read the text Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction, Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Nicholas of Cusa is believed to have been the first to discover the benefits of concave lenses for the treatment of myopia in 1451. Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect

The Abbe sine condition, due to Ernst Abbe (1860s), is a condition that must be fulfilled by a lens or other optical system in order for it to produce sharp images of off-axis as well as on-axis objects. The Abbe sine condition is a condition that must be fulfilled by a lens or other Optical system in order for it to produce sharp images of off-axis as well as on-axis Ernst Karl Abbe ( January 23, 1840 &ndash January 14, 1905) was a German Physicist and professor at the University It revolutionized the design of optical instruments such as microscopes, and helped to establish the Carl Zeiss company as a leading supplier of optical instruments. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are Carl Zeiss ( September 11, 1816 &ndash December 3, 1888) was an Optician commonly known for the company he founded Carl Zeiss

Construction of simple lenses

Most lenses are spherical lenses: their two surfaces are parts, with the same axis as each other, of the surfaces of spheres. Each surface can be convex (bulging outwards from the lens), concave (depressed into the lens), or planar (flat). The line joining the centres of the spheres making up the lens surfaces is called the axis of the lens. Typically the lens axis passes through the physical centre of the lens, because of the way they are manufactured. Lenses may be cut or ground after manufacturing to give them a different shape or size. The lens axis may then not pass through the physical centre of the lens.

Toric or shero-cylindrical lenses have surfaces with two different radii of curvature in two orthogonal planes. In Optics, a toric lens is a type of lens whose surface is a combination of a Sphere and a cylinder. They have a different focal power in different meridians. Optical power ( dioptric power or refractive power) is the degree to which a lens or Mirror converges or diverges light This is a form of deliberate astigmatism. See also Aberration in optical systems, Astigmatism (eye An Optical system with astigmatism is one where rays that propagate

More complex are aspheric lenses. An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a Sphere nor of a circular cylinder. These are lenses where one or both surfaces have a shape that is neither spherical nor cylindrical. Such lenses can produce images with much less aberration than standard simple lenses.

Types of simple lenses

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex, A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses. A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus

If the lens is biconvex or plano-convex, a collimated or parallel beam of light travelling parallel to the lens axis and passing through the lens will be converged (or focused) to a spot on the axis, at a certain distance behind the lens (known as the focal length). Collimated light is Light whose rays are nearly parallel and therefore will spread slowly as it propagates The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. In this case, the lens is called a positive or converging lens.

If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens; the distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens.

Convex-concave (meniscus) lenses can be either positive or negative, depending on the relative curvatures of the two surfaces. A negative meniscus lens has a steeper concave surface and will be thinner at the centre than at the periphery. Conversely, a positive meniscus lens has a steeper convex surface and will be thicker at the centre than at the periphery. An ideal thin lens with two surfaces of equal curvature would have zero optical power, meaning that it would neither converge nor diverge light. In Optics, a thin lens is a lens with a thickness (distance along the Optical axis between the two surfaces of the lens that is negligible compared Optical power ( dioptric power or refractive power) is the degree to which a lens or Mirror converges or diverges light All real lenses have a nonzero thickness, however, which affects the optical power. To obtain exactly zero optical power, a meniscus lens must have slightly unequal curvatures to account for the effect of the lens' thickness.

Lensmaker's equation

The focal length of a lens in air can be calculated from the lensmaker's equation:^[7]

where

f is the focal length of the lens,

n is the refractive index of the lens material,

R₁ is the radius of curvature of the lens surface closest to the light source,

R₂ is the radius of curvature of the lens surface farthest from the light source, and

d is the thickness of the lens (the distance along the lens axis between the two surface vertices). The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis

Sign convention of lens radii R₁ and R₂

Main article: Radius of curvature (optics)

The signs of the lens' radii of curvature indicate whether the corresponding surfaces are convex or concave. Radius of curvature has specific meaning and Sign convention in Optical design. The sign convention used to represent this varies, but in this article if R₁ is positive the first surface is convex, and if R₁ is negative the surface is concave. In Physics, a sign convention is a choice of the signs (plus or minus of a set of quantities in a case where the choice of sign is arbitrary The signs are reversed for the back surface of the lens: if R₂ is positive the surface is concave, and if R₂ is negative the surface is convex. If either radius is infinite, the corresponding surface is flat. Infinity (symbolically represented with ∞) comes from the Latin infinitas or "unboundedness

Thin lens equation

If d is small compared to R₁ and R₂, then the thin lens approximation can be made. In Optics, a thin lens is a lens with a thickness (distance along the Optical axis between the two surfaces of the lens that is negligible compared For a lens in air, f is then given by

^[8]

The focal length f is positive for converging lenses, and negative for diverging lenses. The value 1/f is known as the optical power of the lens, measured in dioptres, which are units equal to inverse meters (m⁻¹). Optical power ( dioptric power or refractive power) is the degree to which a lens or Mirror converges or diverges light A dioptre, or diopter, is a Unit of measurement of the Optical power of a lens or curved Mirror, which is equal to the reciprocal

Lenses have the same focal length when light travels from the back to the front as when light goes from the front to the back, although other properties of the lens, such as the aberrations are not necessarily the same in both directions. Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics.

Imaging properties

As mentioned above, a positive or converging lens in air will focus a collimated beam travelling along the lens axis to a spot (known as the focal point) at a distance f from the lens. In Geometrical optics, a focus, also called an image point, is the point where Light rays originating from a point on the object converge. Conversely, a point source of light placed at the focal point will be converted into a collimated beam by the lens. A point source is a single identifiable localized source of something These two cases are examples of image formation in lenses. An image (from Latin imago) or picture is an artifact usually two-dimensional that has a similar appearance to some subject &mdashusually In the former case, an object at an infinite distance (as represented by a collimated beam of waves) is focused to an image at the focal point of the lens. In the latter, an object at the focal length distance from the lens is imaged at infinity. The plane perpendicular to the lens axis situated at a distance f from the lens is called the focal plane.

If the distances from the object to the lens and from the lens to the image are S₁ and S₂ respectively, for a lens of negligible thickness, in air, the distances are related by the thin lens formula:

.

What this means is that, if an object is placed at a distance S₁ along the axis in front of a positive lens of focal length f, a screen placed at a distance S₂ behind the lens will have a sharp image of the object projected onto it, as long as S₁ > f (if the lens-to-screen distance S₂ is varied slightly, the image will become less sharp). This is the principle behind photography. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing The image in this case is known as a real image. In Optics, a real image is a representation of an actual object (source formed by rays of Light passing through the Image.

Note that if S₁ < f, S₂ becomes negative, the image is apparently positioned on the same side of the lens as the object. Although this kind of image, known as a virtual image, cannot be projected on a screen, an observer looking through the lens will see the image in its apparent calculated position. In Optics, a virtual image is an image in which the outgoing rays from a point on the object never actually intersect at a point A magnifying glass creates this kind of image. magnifying glass (called a hand lens in laboratory contexts is a convex lens which is used to produce a magnified Image of an object

The magnification of the lens is given by:

,

where M is the magnification factor; if |M|>1, the image is larger than the object. Magnification is the process of enlarging something only in appearance not in physical size Notice the sign convention here shows that, if M is negative, as it is for real images, the image is upside-down with respect to the object. For virtual images, M is positive and the image is upright.

In the special case that S₁ = ∞, then S₂ = f and M = −f / ∞ = 0. This corresponds to a collimated beam being focused to a single spot at the focal point. The size of the image in this case is not actually zero, since diffraction effects place a lower limit on the size of the image (see Rayleigh criterion). Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle Angular resolution describes the resolving power of any image forming device such as an optical or Radio telescope, a Microscope, a Camera

The formulas above may also be used for negative (diverging) lens by using a negative focal length (f), but for these lenses only virtual images can be formed.

For the case of lenses that are not thin, or for more complicated multi-lens optical systems, the same formulas can be used, but S₁ and S₂ are interpreted differently. If the system is in air or vacuum, S₁ and S₂ are measured from the front and rear principal planes of the system, respectively. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis Imaging in media with an index of refraction greater than 1 is more complicated, and is beyond the scope of this article.

Aberrations

Main article: Aberration in optical systems

Lenses do not form perfect images, and there is always some degree of distortion or aberration introduced by the lens which causes the image to be an imperfect replica of the object. Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. Careful design of the lens system for a particular application ensures that the aberration is minimized. There are several different types of aberration which can affect image quality.

Spherical aberration

Spherical aberration occurs because spherical surfaces are not the ideal shape with which to make a lens, but they are by far the simplest shape to which glass can be ground and polished and so are often used. spherical-aberration-diskjpg|thumb|300 px|left|A Point source as imaged by a system with negative (top zero (center and positive (bottom spherical aberration Spherical aberration causes beams parallel to, but distant from, the lens axis to be focused in a slightly different place than beams close to the axis. This manifests itself as a blurring of the image. Lenses in which closer-to-ideal, non-spherical surfaces are used are called aspheric lenses. An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a Sphere nor of a circular cylinder. These were formerly complex to make and often extremely expensive, but advances in technology have greatly reduced the manufacturing cost for such lenses. Spherical aberration can be minimised by careful choice of the curvature of the surfaces for a particular application: for instance, a plano-convex lens which is used to focus a collimated beam produces a sharper focal spot when used with the convex side towards the beam.

Coma

Another type of aberration is coma, which derives its name from the comet-like appearance of the aberrated image. In Optics (especially Telescopes, the coma (aka comatic aberration) in an optical system refers to aberration inherent to certain optical A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — Coma occurs when an object off the optical axis of the lens is imaged, where rays pass through the lens at an angle to the axis θ. Rays which pass through the centre of the lens of focal length f are focused at a point with distance f tan θ from the axis. Rays passing through the outer margins of the lens are focused at different points, either further from the axis (positive coma) or closer to the axis (negative coma). In general, a bundle of parallel rays passing through the lens at a fixed distance from the centre of the lens are focused to a ring-shaped image in the focal plane, known as a comatic circle. The sum of all these circles results in a V-shaped or comet-like flare. As with spherical aberration, coma can be minimised (and in some cases eliminated) by choosing the curvature of the two lens surfaces to match the application. Lenses in which both spherical aberration and coma are minimised are called bestform lenses.

Chromatic aberration

Chromatic aberration is caused by the dispersion of the lens material—the variation of its refractive index n with the wavelength of light. In Optics, chromatic aberration is caused by a lens having a different Refractive index for different Wavelengths of Light In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium Since, from the formulae above, f is dependent upon n, it follows that different wavelengths of light will be focused to different positions. Chromatic aberration of a lens is seen as fringes of colour around the image. It can be minimised by using an achromatic doublet (or achromat) in which two materials with differing dispersion are bonded together to form a single lens. An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and Spherical aberration. This reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not produce perfect correction. The use of achromats was an important step in the development of the optical microscope. An apochromat is a lens or lens system which has even better correction of chromatic aberration, combined with improved correction of spherical aberration. Apochromats are much more expensive than achromats.

Different lens materials may also be used to minimize chromatic aberration, such as specialized coatings or lenses made from the crystal fluorite. Fluorite (also called fluorspar) is a Mineral composed of Calcium fluoride, Ca[[Fluorine F2]] This naturally occurring substance has the highest known Abbe number, indicating that the material has low dispersion. In Physics and Optics, the Abbe number, also known as the V-number or constringence of a transparent material is a measure

Other types of aberration

Other kinds of aberration include field curvature, barrel and pincushion distortion, and astigmatism. Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. See also Aberration in optical systems, Astigmatism (eye An Optical system with astigmatism is one where rays that propagate

Aperture diffraction

Even if a lens is designed to minimize or eliminate the aberrations described above, the image quality is still limited by the diffraction of light passing through the lens' finite aperture. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle A diffraction-limited lens is one in which aberrations have been reduced to the point where the image quality is primarily limited by diffraction under the design conditions. The resolution of an optical imaging system like a Microscope or Telescope or Camera can be limited by multiple factors like imperfections in the lenses or misalignment

Compound lenses

See also: Photographic lens, Doublet (lens), and Achromat

Simple lenses are subject to the optical aberrations discussed above. A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with In Optics, a doublet is a type of lens made up of two Simple lenses attached together An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and Spherical aberration. In many cases these aberrations can be compensated for to a great extent by using a combination of simple lenses with complementary aberrations. A compound lens is a collection of simple lenses of different shapes and made of materials of different refractive indices, arranged one after the other with a common axis.

The simplest case is where lenses are placed in contact: if the lenses of focal lengths f₁ and f₂ are "thin", the combined focal length f of the lenses is:

. In Optics, a thin lens is a lens with a thickness (distance along the Optical axis between the two surfaces of the lens that is negligible compared

Since 1/f is the power of a lens, it can be seen that the powers of thin lenses in contact are additive.

If two thin lenses are separated by some distance d, the distance from the second lens to the focal point of the combined lenses is called the back focal length (BFL). This is given by:

.

Note that as d tends to zero, the value of the BFL tends to the value of f given for thin lenses in contact.

If the separation distance is equal to the sum of the focal lengths (d = f₁+f₂), the BFL is infinite. This corresponds to a pair of lenses that transform a parallel (collimated) beam into another collimated beam. This type of system is called afocal, since it produces no net convergence or divergence of the beam. Two lenses at this separation form the simplest type of optical telescope. An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum

Although the system does not alter the divergence of a collimated beam, it does alter the width of the beam. The magnification of the telescope is given by:

,

which is the ratio of the input beam width to the output beam width. Note the sign convention: a telescope with two convex lenses (f₁ > 0, f₂ > 0) produces a negative magnification, indicating an inverted image. A convex plus a concave lens (f₁ > 0 > f₂) produces a positive magnification and the image is upright.

Uses of lenses

A single convex lens mounted in a frame with a handle or stand is a magnifying glass. magnifying glass (called a hand lens in laboratory contexts is a convex lens which is used to produce a magnified Image of an object

Lenses are used as prosthetics for the correction of visual impairments such as myopia, hyperopia, presbyopia, and astigmatism. In Medicine, a prosthesis (plural prostheses) is an Artificial extension that replaces a missing Body part. Visual impairment or vision impairment is Vision loss that constitutes a significant limitation of visual capability resulting from Disease, Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect Hyperopia, also known as farsightedness or longsightedness, is a Defect of vision caused by an imperfection in the Eye (often when Presbyopia (Greek word "presbys" (πρέσβυς meaning "old person" describes the condition where the Eye exhibits a progressively diminished ability See also Aberration in optical systems, Astigmatism (eye An Optical system with astigmatism is one where rays that propagate (See corrective lens, contact lens, eyeglasses. A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the Cornea Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction, ) Most lenses used for other purposes have strict axial symmetry; eyeglass lenses are only approximately symmetric. Axial symmetry is Symmetry around an axis an object is axially symmetric if its appearance is unchanged if rotated around some axis They are usually shaped to fit in a roughly oval, not circular, frame; the optical centers are placed over the eyeballs; their curvature may not be axially symmetric to correct for astigmatism. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain See also Aberration in optical systems, Astigmatism (eye An Optical system with astigmatism is one where rays that propagate Sunglasses lenses may be designed to attenuate light without refraction. Sunglasses or sun glasses are a visual aid variously termed Spectacles or Glasses, which feature lenses that are coloured or darkened to prevent strong

Another use is in imaging systems such as a monocular, binoculars, telescope, spotting scope, telescopic gun sight, theodolite, microscope, camera (photographic lens) and projector. A monocular is a modified Refracting telescope used to Magnify the images of distant objects by passing light through a series of lenses and prisms Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A spotting scope is a portable Telescope, optimized for the observation of terrestrial objects A telescopic sight, commonly called a scope, is a device used to give additional accuracy using a point of aim for Firearms Airguns and Crossbows A theodolite ( is an instrument for measuring both horizontal and vertical Angles as used in Triangulation networks A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are A camera is a device used to capture images either as still Photographs or as sequences of moving images ( Movies or Videos. A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with Some of these instruments produce a virtual image when applied to the human eye; others produce a real image which can be captured on photographic film or an optical sensor. In Optics, a virtual image is an image in which the outgoing rays from a point on the object never actually intersect at a point In Optics, a real image is a representation of an actual object (source formed by rays of Light passing through the Image. This article is mainly concerned with Still photography film For Motion picture film please see Film stock. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument

Convex lenses produce an image of an object at infinity at their focus; if the sun is imaged, all the infrared energy incident on the lens is concentrated on the small image. The Sun (Sol is the Star at the center of the Solar System. A large lens will concentrate enough energy to heat an inflammable object on which the image falls to burning point. Such lenses, which do not need to be even approximately optically accurate, have been used as burning-glasses for hundreds of years. A burning-glass is a large convex lens that can concentrate the Sun 's rays onto a small area heating up the area and thus resulting in ignition of the A modern application is the use of relatively large lenses to concentrate solar energy on relatively small photovoltaic cells, harvesting more energy without the need to use larger, more expensive, cells. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect.

Radio astronomy and radar systems often use dielectric lenses, commonly called a lens antenna to refract electromagnetic radiation into a collector antenna. Radio astronomy is a subfield of Astronomy that studies celestial objects at radio frequencies. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. The Square Kilometre Array radio telescope, scheduled to be operational by 2020[1], will employ such lenses to get a collection area nearly 30 times greater than any previous antenna. The Square Kilometre Array (SKA is a Radio telescope in development which will have a total collecting area of approximately one Square kilometre. A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites

See also

• Aberration in optical systems
• Anti-fogging treatment of optical surfaces
• Axicon
• Back focal plane
• Bokeh
• Cardinal point (optics)
• Corrective lens
• Eyepiece
• F-number
• Fresnel lens
• Gradient index lens
• Gravitational lens
• History of lensmaking
• Lens (anatomy)
• List of lens designs
• Microscope
• Microlens
• Numerical aperture
• Optical coatings
• Optical lens design
• Optical lenticular
• Photochromic lens
• Photographic lens
• Prime lens
• Prism (optics)
• Ray tracing
• Superlens
• Telescope
• Zoom lens

References

General

• Hecht, Eugene (1987). Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. Anti-fog agents also known as anti-fogging agents and treatments prevent the Condensation of Water on a surface in the form of small Droplets An axicon is a specialized type of lens which has a conical surface The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis This article is about the photographic usage of the term "Bokeh" The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus For the device for looking through a camera see Viewfinder. An eyepiece, or ocular lens, is a type of lens that is attached A Fresnel lens (pronounced or) is a type of lens invented by French physicist Augustin-Jean Fresnel. Gradient-index optics is the branch of Optics covering optical effects produced by a gradual variation of the Refractive index of a material A gravitational lens is formed when the light from a very distant bright source (such as a Quasar) is "bent" around a massive object (such as a cluster of Optics began with the development of lenses by the Ancient Egyptians and Mesopotamians followed by theories on Light and vision developed by ancient The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused Achromatic doublet Apochromatic doublet Biconcave lens Biconvex lens Convex-concave A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are Microlenses are small lenses, generally with Diameters less than a Millimetre (mm and often as small as 10 micrometres (µm In Optics, the numerical aperture ( NA) of an optical system is a Dimensionless number that characterizes the range of angles over which the system can accept An optical coating is a thin layer of material deposited on an optical component such as a lens or Mirror, which alters the way in which the optic Optical lens design is the science/art of calculating the various lens construction parameters (variables that will meet or at least approach desired performance requirements Making a lenticular product requires not only a stringency in work and substantial precision throughout the manufacturing process but also a sound knowledge of lenticular optics. Photochromic lenses are lenses that darken on exposure to UV radiation A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with In film and photography a prime lens is either a Photographic lens whose Focal length is fixed as opposed to a Zoom lens, or it is the primary lens In Optics, a prism is a transparent optical element with flat polished surfaces that refract Light. In physics ray tracing is a method for calculating the path of Waves or Particles through a system with regions of varying propagation Velocity, absorption A superlens is a lens which is capable of Subwavelength imaging. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal Optics, 2nd ed. , Addison Wesley. ISBN 0-201-11609-X.   Chapters 5 & 6.
• Greivenkamp, John E. (2004). Field Guide to Geometrical Optics, SPIE Field Guides vol. FG01, SPIE. ISBN 0-8194-5294-7.  

Footnotes

1. ^ Brians, Paul (2003). Common Errors in English.  
2. ^ ^{a b} Whitehouse, David. "World's oldest telescope?", BBC News, 1999-07-01. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) "July 1st" redirects here For the Ayumi Hamasaki song see H (song. Retrieved on 2008-05-10. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1291 - Scottish Nobles recognize the authority of Edward I of England.  
3. ^ D. Brewster (1852). "On an account of a rock-crystal lens and decomposed glass found in Niniveh" (in German). Die Fortschritte der Physik. Deutsche Physikalische Gesellschaft.  
4. ^ Pliny the Elder, The Natural History (trans. Gaius or Caius Plinius Secundus, ( AD 23 – August 25, AD 79 better known as Pliny the Elder, was an ancient Author John Bostock) Book XXXVII, Chap. 10.
5. ^ Pliny the Elder, The Natural History (trans. John Bostock) Book XXXVII, Chap. 16
6. ^ Rashed, R. (1990). "A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses. " Isis, 81, 464–491.
7. ^ Greivenkamp, p. 14; Hecht §6. 1
8. ^ Hecht, § 5. 2. 3

External links

• History of Optics (audio mp3) by Simon Schaffer, Professor in History and Philosophy of Science at the University of Cambridge, Jim Bennett, Director of the Museum of the History of Science at the University of Oxford and Emily Winterburn, Curator of Astronomy at the National Maritime Museum (recorded by the BBC). The University of Cambridge (often Cambridge University) located in Cambridge, England, is the second-oldest university in the The University of Oxford (informally "Oxford University" or simply "Oxford" located in the city of Oxford, Oxfordshire, England is the The National Maritime Museum (NMM in Greenwich, England is the leading Maritime museum of the United Kingdom and may be the largest museum
• a chapter from an online textbook on refraction and lenses
• Thin Spherical Lenses on Project PHYSNET.
• Lens article at digitalartform.com
• Thin Lens Java applet
• Article on Ancient Egyptian lenses
• picture of the Ninive rock crystal lens
• Learning by Simulations - Concave and Convex Lenses

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