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Baris 1:
[[Berkas:LensoBiconvexLens.jpg|thumbjmpl|180px|sebuahLensa lensacembung]]
'''Lensa''' atau '''kanta'''<ref>{{kamus|kanta}}</ref> adalah alat untuk mengumpulkan atau menyebarkan [[cahaya]], biasanya dibentuk dari sepotong kaca yang dibentuk. Alat sejenis digunakan dengan jenis lain dari [[radiasi elektromagnetik]] juga disebut lensa, misalnya, sebuah lensa [[gelombang mikro]] dapat dibuat dari ''[[paraffin wax]]''.
 
Lensa paling awal tercatat di [[Yunani Kuno]], dengan sandiwara [[Aristophanes]] [[The Clouds]] ([[424 SM]]) menyebutkan sebuah [[gelas-pembakar|kaca-pembakar]] (sebuah [[lensa cembung]] digunakan untuk memfokuskan cahaya matahari untuk menciptakan api).
'''Lensa''' atau '''kanta''' adalah sebuah alat untuk mengumpulkan atau menyebarkan [[cahaya]], biasanya dibentuk dari sepotong [[gelas]] yang dibentuk. Alat sejenis digunakan dengan jenis lain dari [[radiasi elektromagnetik]] juga disebut lensa, misalnya, sebuah lensa [[gelombang mikro]] dapat dibuat dari "[[paraffin wax]]".
 
Tulisan [[Pliny the Elder]] ([[23]]-[[79]]) juga menunjukan bahwa gelas-pembakar juga dikenal [[Kekaisaran Roma]], dan disebut juga apa yang kemungkinan adalah sebuah penggunaan pertama dari [[lensa pembetul]]: [[Nero]] juga diketahui menonton [[gladiator]] melalui sebuah [[zamrud]] berbentuk cekung (kemungkinan untuk memperbaiki [[myopia]]).
Lensa paling awal tercatat di [[Sejarah Yunani Kuno|Yunani Kuno]], dengan sandiwara [[Aristophanes]] [[The Clouds]] ([[424 SM]]) menyebutkan sebuah [[gelas-pembakar]] (sebuah lensa konveks digunakan untuk memfokuskan cahaya matahari untuk menciptakan api).
 
[[Seneca the Younger]] ([[3 SM]] - [[65]]) menjelaskan efek pembesaran dari sebuah gelas bulat yang diisi oleh [[air]]. Matematikawan [[muslim]] berkebangsaan [[Bangsa Arab|Arab]] [[Alhazen|Alhazen (Abu Ali al-Hasan Ibn Al-Haitham)]], ([[965]]-[[1038]]) menulis teori optikal pertama dan utama yang menjelaskan bahwa [[lensa mata|lensa]] di [[mata]] manusia membentuk sebuah gambar di [[retina]]. Penyebaran penggunaan lensa tidak terjadi sampai penemuan [[kacamata]], mungkin di [[Italia]] pada [[1280-an]].
Tulisan [[Pliny the Elder]] ([[23]]-[[79]]) juga menunjukan bahwa gelas-pembakar juga dikenal [[Kekaisaran Roma]], dan disebut juga apa yang kemungkinan adalah sebuah penggunaan pertama dari [[lensa pembetul]]: [[Nero]] juga diketahui menonton [[gladiator]] melalui sebuah [[emerald]] berbentuk-konkave (kemungkinan untuk memperbaiki [[myopia]]).
 
== Konstruksi ==
[[Seneca the Younger]] ([[3 SM]] - [[65]]) menjelaskan efek pembesaran dari sebuah gelas bulat yang diisi oleh [[air]]. Matematikawan muslim berkebangsaan [[Bangsa Arab|Arab]] [[Alhazen|Alhazen (Abu Ali al-Hasan Ibn Al-Haitham)]], ([[965]]-[[1038]]) menulis teori optikal pertama dan utama yang menjelaskan bahwa [[lensa (penglihatan)|lensa]] di [[mata]] manusia membentuk sebuah gambar di [[retina]]. Penyebaran penggunaan lensa tidak terjadi sampai penemuan [[kaca mata]], mungkin di [[Italia]] pada [[1280-an]].
Konstruksi lensa yang paling umum adalah '''lensa speris''' ([[bahasa Inggris|en]]: '''''spherical lens'''''), yaitu lensa dengan bidang [[antarmuka]] yang melengkung speris ([[bahasa Inggris|en]]: ''spherical curvature''), yaitu kelengkungan bidang permukaan bola dengan [[radius speris]] ([[bahasa Inggris|en]]: ''radius of curvature'') tertentu. Notasi radius yang digunakan adalah R, akan bernilai positif saat [[antarmuka]] melengkung keluar menjauhi titik pusat lensa dan disebut antarmuka cembung ([[bahasa Inggris|en]]: ''convex''). Notasi negatif akan digunakan untuk antarmuka cekung ([[bahasa Inggris|en]]: ''concave'') yang melengkung ke dalam mendekati titik pusat lensa.
 
=== [[Lensa sederhana]] ===
<!--
[[Berkas:Lens shapes.svg|360px|ka|jmpl|'''1''' - Symmetrical double convex lens.<br>'''2''' - Asymmetrical double-convex lens<br>'''3''' - Plano- convex lens.<br>'''4''' - Positive meniscus lens.<br>'''5''' - Symmetrical biconcave lens.<br>'''6''' - Asymmetrical biconcave lens.<br>'''7''' - Plano-concave lens.<br>'''8''' - Negative meniscus lens.]]
==Lens construction==
'''Lensa sederhana''' ([[bahasa Inggris|en]]: '''''simple lens''''', '''''singlet lens''''') atau sering disebut '''lensa''' saja adalah sebuah lensa tunggal speris.
 
Lensa sederhana dibedakan berdasarkan kelengkungan kedua bidang antarmukanya. Sebuah [[lensa cembung]] ([[bahasa Inggris|en]]: ''biconvex lens'') mempunyai dua bidang antarmuka yang cembung, lensa dengan dua bidang cekung disebut [[lensa cekung]] ([[bahasa Inggris|en]]: ''biconcave lens''). Jika salah satu bidang antarmuka datar (mempunyai radius yang tak berhingga), maka lensa tersebut disebut [[lensa plano cembung]] atau [[lensa plano cekung]]. [[Lensa cembung cekung]] mempunyai satu bidang antarmuka cekung dan satu bidang antarmuka cembung, juga sering disebut [[lensa meniskus]] ([[bahasa Inggris|en]]: ''meniscus lens'').
[[image:lens1.png]]
 
Lensa sederhana sangat rentan terhadap aberasi kromatik dan aberasi optis lainnya.
The most common type of lenses are ''spherical lenses'', which are formed from surfaces that have ''spherical curvature'', that is, the front and back surfaces of the lens can be imagined to be part of the surface of two spheres of given radii, ''R''<sub>1</sub> and ''R''<sub>2</sub>, which are called the ''radius of curvature'' of each surface. The sign of ''R''<sub>1</sub> gives the shape of the front surface of the lens: if ''R''<sub>1</sub> is positive, the surface is ''[[convex]]'' (bulging outwards from the lens). If ''R''<sub>1</sub> is negative, the front surface is ''[[concave]]'' (bulging into the lens). If ''R''<sub>1</sub> is infinite, the surface is flat, or has zero curvature, and is said to be ''plane''. The same is true for the back surface of the lens, except that the sign conversion is reversed: if ''R''<sub>2</sub> is positive, it is concave, and if ''R''<sub>2</sub> is negative,the back surface is convex. The line joining the centres of the spheres making up the lens surfaces is called the ''axis'' of the lens; in almost all cases the lens axis passes through the physical centre of the lens.
 
==== [[Lensa cembung]] ====
[[image:lens2.png]]
[[Berkas:lens3b.svg|360px|jmpl|Diagram penelusuran sinar untuk sebuah lensa konvergen]]
<!--[[Berkas:lens1.png|thumb|right|Lensa cembung]]-->
[[Berkas:lens1b.png|jmpl|ka|Lensa cekung]]
Lensa cembung adalah jenis lensa yang memiliki bagian tengah yang lebih tebal dibandingkan bagian pinggir lensanya.
Pada lensa cembung, sinar yang merambat melalui kedua antarmuka akan dibiaskan (terfokus) menuju ke satu titik pada sumbu optis lensa, yang disebut [[jarak fokus]] ([[bahasa Inggris|en]]: ''focal length''). Lensa cembung dalam bahasa Inggris juga disebut ''positive lens'' atau ''converging lens''. Lensa cembung membentuk ''focal point'' pada sisi berlawanan dengan persamaan ''lens maker'':<ref name=hecht>{{cite book|author=E. Hecht|year=1987|title=Optics|url=https://archive.org/details/optics0000hech|edition=2nd|publisher=Addison Wesley|isbn=020111609X}} Chapters 5 & 6.</ref>
 
:<math>\frac{1}{S_1} + \frac{1}{S_2} = \frac{1}{f} </math>
Lenses are classified by the curvature of these two surfaces. A lens is ''biconvex'' (or just ''convex'') if both surfaces are convex, likewise, a lens with two concave surfaces is ''biconcave'' (or ''concave''). If one of the surfaces is flat, the lens is termed ''plano-convex'' or ''plano-concave'' depending on the curvature of the other surface. A lens with one convex and one concave side is termed ''convex-concave'', and in this case if both curvatures are equal it is a ''meniscus'' lens. (Sometimes, all lenses of the convex-concave type are called meniscus lenses.)
 
di mana:
If the lens is biconvex or plano-convex, a [[collimated]] or parallel beam of light passing along the lens axis and 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]]''). In this case, the lens is called a ''positive'' or ''converging'' lens.
* <math>S_2</math> adalah jarak [[citra]] dan sesuai konvensi, bernilai negatif pada sisi yang sama dengan subyek<ref name=hecht />
* <math>f</math> adalah 'rentang vokal, bernilai negatif untuk lensa cekung
 
dan persamaan magnifikasi lensa:
[[image:lens1b.png]]
 
:<math>M = - \frac{S_2}{S_1} = \frac{f}{f - S_1}</math>
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.
 
Lensa cembung bersifat konvergen dan nilai fokusnya positif.
If the lens is convex-concave, whether it is converging or diverging depends on the relative curvatures of the two surfaces. If the curvatures are equal (a meniscus lens), then the beam is neither converged nor diverged.
 
Lensa cembung (bernilai positif atau konvers) terdiri dari 3 jenis yaitu:
The value of the focal length ''f'' for a particular lens can be calculated from the ''lensmaker's equation'':
* Cermin cembung (bikonveks)
* Cembung datar (plankonveks)
* Cembung cekung (konkaf–konveks)
 
==== [[Lensa cekung]] ====
:<math>\frac{1}{f} = \left(\frac{n}{n'}-1\right) \left[ \frac{1}{R_1} + \frac{1}{R_2} + \frac{(n-1)d}{n R_1 R_2} \right],</math>
Lensa cekung adalah jenis lensa yang memiliki bagian tengah yang lebih tipis dibandingkan bagian pinggir lensanya.
Pada lensa cekung, sinar cahaya yang merambat akan dibiaskan menjauhi dari [[Sumbu optis|sumbu optis lensa]] ke arah pinggir lensa dengan proyeksi imajiner sinar menuju ke satu titik, seperti pada gambar.
 
Lensa cekung bersifat [[divergen]] atau dengan kata lain menyebarkan berkas sinar cahaya dan titik fokus lensa cekung terletak pada sisi yang sama dengan berkas sinar cahaya sehingga titik fokus lensa cekung memiliki sifat mata atau semu dan nilai fokusnya negatif.
where ''n'' is the [[refractive index]] of the lens material, ''n''' is the refractive index of the place which the lens is in and ''d'' is the distance along the lens axis between the two surfaces (known as the thickness of the lens). If ''d'' is small compared to ''R''<sub>1</sub> and ''R''<sub>2</sub>, then the ''thin lens'' assumption can be made, and ''f'' can be estimated as:
 
Lensa cekung (bernilai negatif atau konkaf) terdiri dari 3 jenis yaitu:
:<math>\frac{1}{f} = \left(\frac{n}{n'}-1\right)\left[ \frac{1}{R_1} + \frac{1}{R_2} \right].</math>
* Cermin cekung (bikonkaf)
* Cekung datar (plankonkaf)
* Cembung cekung(konveks–konkaf)
 
{| class="wikitable"
The focal length ''f'' is positive for converging lenses, negative for diverging lenses, and infinite for meniscus lenses. The value 1/''f'' is known as the ''power'' of the lens, and so meniscus lenses are said to have zero power. Lens power is measured in ''[[dioptre]]s'', which have units of inverse meters (''m''<sup>−1</sup>).
|-
! Ruang Benda !! Ruang Bayangan !! Letak bayangan !! Sifat bayangan
|-
| I || IV || depan || maya, tegak, diperbesar
|-
| II || III || belakang || nyata, terbalik, diperbesar
|-
| III || II || belakang || nyata, terbalik, diperkecil
|-
| IV || I || depan || maya, tegak, diperkecil
|-
| f || ~ || - || tidak terbentuk bayangan
|-
| R || R || belakang || nyata, terbalik, sama besar
|}
 
==== [[Lensa meniskus]] ====
Lenses are also reciprocal; i.e. they have the same focal length when light travels from the front to the back as when light goes from the back to the front (although other properties of the lens, such as the aberration [see below] are not necessarily the same in both directions).
Lensa meniskus ([[bahasa Inggris|en]]: '''''meniscus lens''''', '''''ophthalmic lens''''') atau [[lensa cembung cekung]], dapat berupa lensa positif atau negatif yang bergantung pada radius speris kedua bidang antarmuka. Pada nilai radius speris yang sama besar, sinar yang merambat tidak akan dibiaskan. Lensa meniskus positif akan membiaskan sinar seperti lensa cembung, lensa ini mempunyai bidang antarmuka cembung dengan radius speris yang lebih kecil. Sebaliknya lensa meniskus negatif mempunyai bidang antarmuka cekung dengan radius speris yang lebih kecil.
 
==== [[Lensa tipis]] ====
==Imaging properties==
'''Lensa tipis''' ([[bahasa Inggris|en]]: '''''thin lens''''') adalah sebuah lensa dengan ketebalan yang sangat kecil jika dibandingkan dengan nilai [[jarak fokus]]nya.
 
=== [[Lensa asperis]] ===
As mentioned above, a positive or converging lens 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. Conversely, a point source of light placed at the focal point will be converted into a collimated beam by the lens. These two cases are examples of ''image'' formation in lenses. In the former case, an object at an infinite distance (as represented by a collimated beam of light) 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''.
[[Berkas:Pfeilhöhe.svg|jmpl|ka|Sebuah lensa cembung asperis.]]
[[Berkas:Fresnel lens.svg|jmpl|220px|1: Penampang lensa Fresnel<br />2: Penampang lensa plano konveks dengan daya yang sama]]
'''Lensa asperis''' ([[bahasa Inggris|en]]: '''''aspheric lens''''', '''''asphere''''') yang mempunyai bidang antarmuka dengan kelengkungan bidang yang bukan merupakan bidang permukaan bola. Sebuah lensa asperis dapat mengurangi [[aberasi speris]] atau [[aberasi optis]] lainnya, atau menggantikan kinerja beberapa jajaran lensa.
 
=== [[Lensa aksikon]] ===
[[image:lens3.png]]
'''Lensa aksikon''' ([[bahasa Inggris|en]]: '''''axicon lens''''') adalah lensa dengan bidang antarmuka berbentuk kerucut. Lensa aksikon akan memproyeksikan sebuah titik menjadi garis sepanjang sumbu optis, dan mengubah sinar [[laser]] menjadi bentuk cincin.<ref>{{cite web| url=http://www.optics.arizona.edu/OPTI696/2005/axicon_Proteep.pdf| author=Proteep Mallik| title=The Axicon| year=2005| accessdate=2007-11-22| archive-date=2009-11-23| archive-url=https://web.archive.org/web/20091123101108/http://www.optics.arizona.edu/OPTI696/2005/axicon_Proteep.pdf| dead-url=yes}}</ref> Lensa ini dapat dipergunakan untuk mengubah [[sorot Gauss]] menjadi seperti [[sorot Bessel]] dengan efek [[difraksi]] yang sangat kecil.<ref>{{cite web| url=http://www.st-andrews.ac.uk/%7Eatomtrap/papers/Nature.pdf| author=Kishan Dholakia| coauthors=David McGloin, and Vene Garcés-Chávez| title=Optical micromanipulating using a self-reconstructing light beam| year=2002| accessdate=2007-11-22| archive-date=2004-12-04| archive-url=https://web.archive.org/web/20041204141219/http://www.st-andrews.ac.uk/~atomtrap/papers/Nature.pdf| dead-url=yes}}</ref><ref>{{cite journal| author=V. Garcés-Chávez| coauthors=D. McGloin, H. Melville, W. Sibbett and K. Dholakia| title=Simultaneous micromanipulation in multiple planes using a self-reconstructing light beam| journal=Nature| volume=419| year=2002| url=http://sinclair.ece.uci.edu/Papers/Optics/Orbital%20angular%20momentum/Garces-Chavez%20Nature%20419%20pp145-148%202002%20(Simultaneous%20micromanipulation%20in%20multiple%20planes%20using%20a%20self-reconstructing%20light%20beam).pdf| accessdate=2007-02-06| doi=10.1038/nature01007| pages=145| archive-date=2006-09-19| archive-url=https://web.archive.org/web/20060919043112/http://www.st-andrews.ac.uk/~atomtrap/papers/Nature.pdf| dead-url=yes}}</ref>
 
=== [[Lensa Fresnel]] ===
If the distances from the object to the lens and from the lens to the image are ''S''<sub>1</sub> and ''S''<sub>2</sub> respectively, for a lens of negligible thickness they are found by the ''thin lens formula'':
'''Lensa Fresnel''' adalah sebuah lensa yang dikembangkan oleh seorang fisikawan berkebangsaan Prancis, [[Augustin Jean Fresnel]] untuk aplikasi pada [[mercusuar]]. Konstruksi lensa didesain dengan panjang fokus yang pendek, jarak fokus tak terhingga dan tebal lensa yang sangat tipis jika dibandingkan dengan lensa konvensional, agar dapat melewatkan lebih banyak [[cahaya]] sehingga lampu mercusuar dapat terlihat dari jarak yang lebih jauh.
 
Menurut majalah Smithsonian, lensa Fresnel yang pertama digunakan pada tahun 1823 pada [[mercusuar Cordouan]] di tanjung [[muara Gironde]], sinar cahaya yang dipancarkan mampu terlihat dari jarak 20 mil (32&nbsp;km).<ref>Watson, Bruce. [http://libproxy.uncg.edu:2088/servlet/BioRC "Science Makes a Better Lighthouse Lens."]{{Pranala mati|date=Februari 2021 |bot=InternetArchiveBot |fix-attempted=yes }} ''Smithsonian''. August 1999 v30 i5 p30. produced in ''Biography Resource Center''. Farmington Hills, Mich.: Thomson Gale. 2005.</ref> Seorang fisikawan [[Skotlandia]], [[Sir David Brewster]], memperkenalkan lensa ini untuk digunakan pada seluruh mercusuar di daratan [[Inggris]].<ref>[http://search.eb.com/eb/article-9016395 "Brewster, Sir David."] ''Encyclopædia Britannica''. 2005. Encyclopædia Britannica Online. 11 November 2005.</ref><ref>[http://libproxy.uncg.edu:2088/servlet/BioRC "David Brewster."]{{Pranala mati|date=Februari 2021 |bot=InternetArchiveBot |fix-attempted=yes }} ''World of Invention'', 2nd ed. Gale Group, 1999. Reproduced in ''Biography Resource Center''. Farmington Hills, Mich.: Thomson Gale. 2005.</ref>
:<math>\frac{1}{S_1} + \frac{1}{S_2} = \frac{1}{f}</math>.
 
Sebelum lensa Fresnel ditemukan, ide untuk membuat lensa yang lebih tipis dan ringan yang tersusun dari beberapa bagian terpisah dalam sebuah bingkai, sering disebut sebagai ide dari [[Georges Louis Leclerc]] dan [[Comte de Buffon]].<ref>[http://search.eb.com/eb/article-9035385 "Fresnel lens."] ''Encyclopædia Britannica''. 2005. Encyclopædia Britannica Online. 11 November 2005.</ref> [[Augustin Jean Fresnel|Fresnel]] menyempurnakan penyusunan lensa-lensa konsentrik tersebut berdasarkan perhitungan [[zona Fresnel]].
What this means is that, if an object is placed at a distance ''S''<sub>1</sub> along the axis in front of a positive lens of focal length ''f'', a screen placed at a distance ''S''<sub>2</sub> behind the lens will have an image of the object projected onto it, as long as ''S''<sub>1</sub> &gt; ''f''. This is the principle behind [[photography]]. The image in this case is known as a ''[[real image]]''.
 
Lensa Fresnel terbagi menjadi 6 kategori berdasarkan panjang fokusnya. Kategori yang pertama merupakan lensa yang terbesar dengan panjang fokus 920&nbsp;mm (36 inci). Kategori yang terakhir dengan lensa terkecil mempunyai panjang fokus 150&nbsp;mm (5,9 inci).<ref>{{cite web
[[image:lens3b.png]]
|url=http://memory.loc.gov/cgi-bin/displayPhoto.pl?path=/pnp/habshaer/ri/ri0300/ri0392/sheet&topImages=00008a.gif&topLinks=00008r.tif,00008a.tif
|title=Fresnel Orders
|accessdate=2007-06-01
|author=Mabel A. Baiges
|year=1988
|format=TIFF}}</ref><ref>{{cite web|title=Fresnel lenses|url=http://www.marinecitymich.org/Blank%20Page.htm|archive-url=https://web.archive.org/web/20070927021951/http://www.marinecitymich.org/Blank%20Page.htm|archive-date=2007-09-27|dead-url=yes|accessdate=2007-06-01}} Note the transcription error in the "Comparative Table of Lens Orders; the "oil consumption per hour" columns should be titled [[Gram|grams]] and [[Fluid ounce|ounces]], not gallons.</ref><ref>{{cite web
|url=http://www.michiganlights.com/fresnel.htm
|title=Fresnel lenses
|accessdate=2008-08-01}}</ref> Pengembangan lensa Fresnel lebih lanjut menambahkan dua kategori lensa yang baru yaitu [[lensa Fresnel mesoradial]] dan [[lensa Fresnel hyper radial|hyper radial]].
 
=== [[Lensa fotokromik]] ===
Note that if ''S''<sub>1</sub> &lt; ''f'', ''S''<sub>2</sub> becomes negative, and 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. A [[magnifying glass]] creates this kind of image.
'''Lensa fotokromik''' ([[bahasa Inggris|en]]: '''''photochromic lens''''') adalah lensa yang menjadi gelap saat terpajan (terpapar) [[sinar]] [[ultraviolet]]. Lensa perlahan kembali menjadi jernih seiring sirnanya pajanan sinar UV tersebut.
 
=== [[Lensa silindris]] ===
The ''magnification'' of the lens is given by:
'''Lensa silindris''' adalah sebuah lensa yang membiaskan sinar cahaya yang merambat melalui mediumnya hingga terfokus pada sebuah garis, bukan pada sebuah titik seperti pada umumnya lensa cembung.
 
=== [[Lensa komposit]] ===
:<math> M = - \frac{S_2}{S_1} = \frac{f}{f - S_1}</math>,
[[Berkas:Achromat doublet en.svg|ka|jmpl|Sebuah lensa doublet akromatika.]]
[[Berkas:Barlow lens.svg|jmpl|Sorot cahaya tanpa (merah) dan dengan (hijau) lensa Barlow]]
[[Berkas:Taylor-Cooke Triplet.svg|jmpl|ka|Lensa Cooke triplet]]
'''Lensa komposit''' adalah jajaran beberapa lensa yang disusun sedemikian rupa untuk memberikan efek sinar cahaya tertentu. Lensa komposit dapat terdiri dari dua buah lensa tunggal atau lebih.
 
==== [[Lensa doublet]] ====
where ''M'' is the magnification factor; if |''M''|&gt;1, the image is larger than the object.
'''Lensa doublet''' adalah sebuah istilah yang digunakan pada bidang [[optika]] untuk menjelaskan sebuah lensa komposit yang terdiri dari dua buah lensa sederhana dengan berbagai macam kombinasinya. Lensa doublet yang paling umum adalah [[lensa doublet akromatika]] yang dapat meredam [[aberasi kromatika]] dengan sangat optimal.
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.
 
==== [[Lensa Barlow]] ====
In the special case that ''S''<sub>1</sub> = ∞, we have ''S''<sub>2</sub> = ''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]]).
'''Lensa Barlow''' adalah sebuah lensa komposit yang ditemukan oleh seorang insinyur berkebangsaan [[Inggris]] bernama [[Peter Barlow]] yang digunakan untuk meningkatkan [[bukaan (fotografi)|bukaan]] suatu sistem optika. Lensa Barlow biasa diletakkan persis sebelum [[jendela bidik]] ([[bahasa Inggris|en]]: ''viewfinder'') untuk meningkatkan [[jarak fokus]] jendela bidik.
 
==== [[Lensa Cooke triplet]] ====
[[image:lens4.png]]
'''Lensa Cooke triplet''' adalah lensa komposit yang dipatenkan oleh [[Dennis Taylor]], seorang insinyur yang bekerja pada perusahaan [[Cooke of York]] pada tahun 1893. Lensa Cooke triplet adalah lensa komposit pertama yang berhasil meminimumkan [[aberasi optis]].
 
==== [[Lensa Dialyt]] ====
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.
'''Lensa Dialyt''' adalah sebuah lensa komposit yang terdiri dari empat buah lensa tunggal yang didesain untuk meredam berbagai macam [[aberasi optis]]. Sebuah lensa komposit serupa dikembangkan oleh [[Taylor Hobson]] dari desain lensa Cooke triplet dan kemudian disebut [[lensa Aviar]]. Sedangkan [[lensa Celor]] adalah desain lensa Dialyt yang telah mengalami penyempurnaan.
 
==Aberrations Referensi ==
{{reflist}}
* {{cite book|first=Eugene|last=Hecht|year=1987|title=Optics|url=https://archive.org/details/optics0000hech|edition=2nd|publisher=Addison Wesley|isbn=0-201-11609-X}} Chapters 5 & 6.
* {{cite book|first=Eugene|last=Hecht|year=2002|title=Optics|edition=4th|publisher=Addison Wesley|isbn=0-321-18878-0}}
* {{cite book|first=John E.|last=Greivenkamp|year=2004|title=Field Guide to Geometrical Optics|url=https://archive.org/details/fieldguidetogeom0000grei|publisher=SPIE|others=SPIE Field Guides vol. '''FG01'''|isbn=0-8194-5294-7 }}
*https://bangid000.blogspot.com/2020/03/teori-fisika-dalam-anime-dr.html?m=1 Teori fisika di Dr Stone.
 
== Bacaan lain ==
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. Careful design of the lens system for a particular application ensures that the aberration is minimised. There are several different types of aberration which can affect image quality.
* "The Fresnel Lens." The Keeper's Log (Winter 1985), pp.&nbsp;12–14.
 
* [http://www.uscg.mil/History/weblighthouses/aton_lighthousebib.html Lighthouses, Illuminants, Lenses Engineering and Augustin Fresnel, An Historical Bibliography, United States Coast Guard.]
[[image:lens5.png]]
* [[United States Coast Guard]], ''Aids to Navigation'', (Washington, DC: U. S. Government Printing Office, 1945).
 
* [http://www.uscg.mil/History/weblighthouses/h_lhbib.asp United States Coast Guard, ''Aids to Navigation Historical Bibliography''.]
===Spherical aberration===
* [http://www.uscg.mil/history/docs/CG_Classical_Lens_in_Operation.pdf United States Coast Guard, Fresnel Lenses Still in Operation.]
''Spherical aberration'' is caused 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 causes beams parallel to but away 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, which are complex to make and often extremely expensive. 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.
 
[[image:lens-coma.png]]
 
===Coma===
Another type of aberration is ''coma'', which derives its name from the [[comet]]-like appearance of the aberrated image. 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.
 
[[image:lens6a.png]]
[[image:lens6b.png]]
 
===Chromatic aberration===
''[[Chromatic aberration]]'' is caused by the [[dispersion (optics)|dispersion]] of the lens material, the variation of its [[refractive index]] ''n'' with the wavelength of light. Since from the formulae above ''f'' is dependent on ''n'', if follows that different wavelengths of light will be focused to different positions. Chromatic aberration of a lens is seen as fringes of color 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. 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 minimizes both chromatic and spherical aberrations.
 
Other kinds of aberration include ''field curvature'', ''barrel'' and ''pincushion distortion'', and ''astigmatism''.
 
==Multiple lenses==
 
Lenses may be combined to form more complex optical systems. The simplest case is when lenses are placed in contact: if the lenses of focal lengths ''f''<sub>1</sub> and ''f''<sub>2</sub> are "thin", the combined focal length ''F'' of the lenses can be calculated from:
 
:<math>\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}</math>.
 
Since 1/''f'' is the power of a lens, it can be seen that the powers of thin lenses in contact are additive.
 
== Uses of lenses ==
 
One important use of lenses is as a [[prosthetic]] for the correction of [[visual impairment]]s such as [[myopia]], [[hyperopia]], [[presbyopia]], and [[astigmatism]]. See [[corrective lens]], [[contact lens]], [[eyeglasses]].
 
Another use is in imaging systems such as a [[monocular]], [[binoculars]], [[telescope]], [[spotting scope]], [[scope (disambiguation)|telescopic gun sight]], [[theodolite]], [[microscope]], and [[camera]] ([[photographic lens]]). A single convex lens mounted in a frame with a handle or stand is a [[magnifying glass]].
 
[[Radio astronomy]] and [[radar]] systems often use [[dielectric lens|dielectric lenses]], commonly called a [[lens antenna]] to refract [[electromagnetic radiation]] into a collector antenna. The [[Square Kilometer Array]] [[radio telescope]] will employ such lenses to get a collection area nearly 30 times greater than what is currently the largest antenna ever built.
-->
 
== Lihat pula ==
 
* [[Aberration in optical systems]]
* [[Lensa fotografi]]
* [[Bukaan (fotografi)|Bukaan]]
* [[abgka-F]]
* [[Numerical ApertureCermin]]
* [[Tingkap numeris]]
* [[Bokeh]]
* [[Teleskop]]
* [[Mikroskop]]
* [[Eyepiece]]
* [[Lensa Fresnel]]
* [[Pelapisan optik]]
* [[Gradient index lens]]
Baris 129 ⟶ 161:
== Pranala luar ==
{{Commons|Lens}}
* [http://www.digitalartform.com/lenses.htm Lens article at ''digitalartform.com''] {{Webarchive|url=https://web.archive.org/web/20160304054022/http://www.digitalartform.com/lenses.htm |date=2016-03-04 }}
* [http://www.phy.ntnu.edu.tw/java/Lens/lens_e.html Thin Lens Java applet]
* [http://home.comcast.net/~hebsed/enoch.htm Article on Ancient Egyptian lenses]
* [http://lighthousegetaway.com/lights/fresnel.html Lighthouse Getaway: Fresnel lens] (contains photographs.)
* {{cite web|url=http://www.terrypepper.com/lights/index.htm |author=Pepper, Terry|title=''Seeing the Light: Lighthouses on the western Great Lakes''}}
* [http://www-personal.umich.edu/~bclee/lens.html Random Destructive Acts via Focused Solar Radiation.]
* [http://www.truckview.net TruckView Fresnel lens combats the HGV Blind-Spot.] {{Webarchive|url=https://web.archive.org/web/20190408105246/http://www.truckview.net/ |date=2019-04-08 }}
* [http://vega.org.uk/video/programme/226 How the Fresnel lens works.]
* [http://www.digitalartform.com/archives/2009/04/fresnel_lens_-.html A computer analysis of the Fresnel lens cross section depicted in the 'graphic examples' section of this very Wikipedia article.] {{Webarchive|url=https://web.archive.org/web/20090520054046/http://www.digitalartform.com/archives/2009/04/fresnel_lens_-.html |date=2009-05-20 }}
* [http://books.google.com/books?id=cuzYl4hx-B8C&pg=PA58&lpg=PA58&dq=Fused+quartz+nikon++camera+lens&source=web&ots=n-IqvTABOz&sig=t-YYBNAIsgKQ37D9kTA0CcK6f1k&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PPA100,M1 Applied photographic optics Book]
* [http://books.google.com/books?id=J0RX1mbhzAEC&printsec=toc&dq=bk7+optical+glass+construction&source=gbs_summary_s&cad=0#PRA1-PA58,M1 Book- The properties of optical glass]
* [http://books.google.com/books?id=_T9dX14rz64C&pg=PT415&lpg=PT415&dq=camera++optical+glass++composition&source=web&ots=YMMv0GjGDL&sig=8VZXryxlUfcVq3nonFvrNWElkoI&hl=en&sa=X&oi=book_result&resnum=7&ct=result Handbook of Ceramics, Glasses, and Diamonds]
* [http://books.google.com/books?id=KdYclkhSfTAC&pg=PT49&lpg=PT49&dq=optical+glass+ingredients&source=web&ots=sLEkmvi05g&sig=F6ERFbklTewIvFuKh30POTb0JG0&hl=en&sa=X&oi=book_result&resnum=7&ct=result Optical glass construction]
* [http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20070301.shtml History of Optics (audio mp3)] {{Webarchive|url=https://web.archive.org/web/20090106072032/http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20070301.shtml |date=2009-01-06 }} 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]]).
* [http://www.lightandmatter.com/html_books/5op/ch04/ch04.html a chapter from an online textbook on refraction and lenses] {{Webarchive|url=https://web.archive.org/web/20091217113846/http://www.lightandmatter.com/html_books/5op/ch04/ch04.html |date=2009-12-17 }}
* [http://www.physnet.org/modules/pdfmodules/m223.pdf ''Thin Spherical Lenses ''] on [http://www.physnet.org Project PHYSNET].
* [http://www.digitalartform.com/lenses.htm Lens article at ''digitalartform.com''] {{Webarchive|url=https://web.archive.org/web/20160304054022/http://www.digitalartform.com/lenses.htm |date=2016-03-04 }}
* [http://home.comcast.net/~hebsed/enoch.htm Article on Ancient Egyptian lenses]
*[https://designeroptics.com/blogs/news/can-i-get-bifocal-prescription-sunglasses-what-you-need-to-know Detailed analysis of bifocal prescription lenses]
* [http://www3.usal.es/%7Ehistologia/aplicacion/english/museum/microsco/micros01/micros01.htm picture of the Ninive rock crystal lens] {{Webarchive|url=https://web.archive.org/web/20070516051709/http://www3.usal.es/%7Ehistologia/aplicacion/english/museum/microsco/micros01/micros01.htm |date=2007-05-16 }}
* [http://luminous-landscape.com/tutorials/resolution.shtml Do Sensors “Outresolve” Lenses?] {{Webarchive|url=https://web.archive.org/web/20100102070908/http://luminous-landscape.com/tutorials/resolution.shtml |date=2010-01-02 }}; on lens and sensor resolution interaction.
 
== Simulasi ==
{{Link FA|ru}}
[[Berkas:ThinLens.gif|jmpl|ka|Thin lens simulation]]
* [http://www.phy.ntnu.edu.tw/java/Lens/lens_e.html Thin Lens Java applet]
* [http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1155msg4448;topicseen#msg4448 Open source thin lens simulation] (Java applet)
* [http://www.vias.org/simulations/simusoft_lenses.html Learning by Simulations] - Concave and Convex Lenses
* [http://www.arachnoid.com/OpticalRayTracer/ OpticalRayTracer - [[GPL|Open source]] lens simulator (downloadable java)]
 
[[Kategori:Lensa| ]]
[[Kategori:OptikOptika]]
[[Kategori:Optika geometris]]
 
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