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Magnifying glass
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<h2 id="use">Use</h2> <p class="note">See also: <a href="/facts/Burning_glass/uPp2qwxs">Burning glass</a></p> <p>The <a href="/facts/Lens_(optics)/ejlH6n5c">convex lens</a> of a magnifying glass can be used to produce a <a href="/facts/Magnification/ACFaV1Bd">magnified</a> <a href="/facts/Image/hbjEdTXK">image</a> of an object. A magnifying glass can also be used to focus light, such as to concentrate the Sun's radiation to create a hot spot at the <a href="/facts/Focus_(optics)/QuRKfhg6">focus</a> for fire starting.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <h3>Magnification</h3> <p class="note">Main article: <a href="/facts/Magnification/ACFaV1Bd">Magnification</a></p> <p>The <a href="/facts/Magnification/ACFaV1Bd">magnification</a> of a magnifying glass depends upon where it is placed between the user's eye and the object being viewed, and the total distance between them. The <i>magnifying power</i> is equivalent to <a href="/facts/Angular_magnification/ACFaV1Bd">angular magnification</a> (this should not be confused with <a href="/facts/Optical_power/jmIWyX25">optical power</a>, which is a different quantity). The magnifying power is the ratio of the sizes of the images formed on the user's retina with and without the lens.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> For the "without" case, it is typically assumed that the user would bring the object as close to one eye as possible without it becoming blurry. This point, known as the <i>near point of <a href="/facts/Accommodation_(eye)/UqjPBp3S">accommodation</a></i>, varies with age. In a young child, it can be as close as 5 cm, while, in an elderly person it may be as far as one or two metres. Magnifiers are typically characterized using a "standard" value of 0.25 m. </p><p>The highest magnifying power is obtained by putting the lens very close to one eye, and moving the eye and the lens together to obtain the best <a href="/facts/Focus_(optics)/QuRKfhg6">focus</a>. The object will then typically also be close to the lens. The magnifying power obtained in this condition is <i>MP</i>0 = <i>d</i>oΦ + 1, where Φ is the optical power in <a href="/facts/Dioptre/as62tso3">dioptres</a> and <i>d</i>o is the <a href="/facts/Near_point/3krr6hEq">near point</a> of the eye, which is typically assumed to be 0.25 m.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> This value of the magnifying power is the one normally used to characterize magnifiers. It is typically denoted "<i>m</i>×", where <i>m</i> = <i>MP</i>0. This is sometimes called the <i>total power</i> of the magnifier (not to be confused with optical power). </p><p>Magnifiers are not always used as described above because it is more comfortable to put the magnifier close to the object (one focal length away). The eye can then be a larger distance away, and a good image can be obtained very easily; the focus is not very sensitive to the eye's exact position. The magnifying power in this case is roughly <i>MP</i> = <i>d</i>oΦ.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p><p>A typical magnifying glass might have a <a href="/facts/Focal_length/brGIUkEY">focal length</a> of 25 cm, corresponding to an optical power of 4 dioptres. Such a magnifier would be sold as a "2×" magnifier. In actual use, an observer with "typical" eyes would obtain a magnifying power between 1 and 2, depending on where lens is held. The dependence on the value of near point means that an older person obtains more magnification from a magnifying glass than a young person does. </p> <h2 id="history">History</h2> <p>"The evidence indicates that the use of lenses was widespread throughout the Middle East and the Mediterranean basin over several millennia".<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Archaeological findings from the 1980s in Crete's Idaean Cave unearthed rock crystal lenses dating back to the <a href="/facts/Archaic_Greece/pWyHxf6H">Archaic Greek period</a>, showcasing exceptional optical quality. These discoveries suggest that the use of lenses for magnification and possibly for starting fires was widespread in the Mediterranean and Middle East, indicating an advanced understanding of optics in <a href="/facts/Classical_antiquity/JBq8vEX9">antiquity</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The earliest explicit written evidence of a magnifying device is a joke in <a href="/facts/Aristophanes/xbpAcg6F">Aristophanes</a>'s <i><a href="/facts/The_Clouds/A2dbGuo7">The Clouds</a></i><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> from 424 BC, where magnifying lenses to ignite tinder were sold in a pharmacy, and <a href="/facts/Pliny_the_Elder/grx67ghR">Pliny the Elder</a>'s "lens",<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> a glass globe filled with water, used to cauterize wounds. (<a href="/facts/Seneca_the_Younger/ND2lmLUv">Seneca</a> wrote that it could be used to read letters "no matter how small or dim".<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a>) </p><p>A convex lens used for forming a magnified image was described in the <i><a href="/facts/Book_of_Optics/SmYrlPcg">Book of Optics</a></i> by <a href="/facts/Ibn_al-Haytham/Q5H9hm4J">Ibn al-Haytham</a> in 1021.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>[<i>verification needed</i>] After the book was translated during the <a href="/facts/Latin_translations_of_the_12th_century/cd1jRx5z">Latin translations of the 12th century</a>, <a href="/facts/Roger_Bacon/p1kvowog">Roger Bacon</a> described the properties of a magnifying glass in 13th-century <a href="/facts/England/U9mE5bGL">England</a>. This was followed by the development of <a href="/facts/Eyeglasses/ER3sFKmJ">eyeglasses</a> in 13th-century <a href="/facts/Italy/tUf0PDYF">Italy</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> In the late 1500s, two Dutch spectacle makers <a href="/facts/Jacob_Metius/wveloAhS">Jacob Metius</a> and <a href="/facts/Zacharias_Janssen/8H1CAgbK">Zacharias Janssen</a> crafted the <a href="/facts/Compound_microscope/5700vcna">compound microscope</a> by assembling several magnifying lenses in a tube. <a href="/facts/Hans_Lipperhey/L9E7c5c2">Hans Lipperhey</a> introduced the <a href="/facts/Telescope/BDwYahhR">telescope</a> in 1608 and <a href="/facts/Galileo_Galilei/98VT2z3v">Galileo Galilei</a> improved on the device in 1609.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <h2 id="alternatives">Alternatives</h2> <p>Magnifying glasses typically have low magnifying power: 2×–6×, with the lower-power types being much more common. At higher magnifications, the image quality of a simple magnifying glass becomes poor due to <a href="/facts/Optical_aberrations/YIqd9cA8">optical aberrations</a>, particularly <a href="/facts/Spherical_aberration/x7V1JMQ9">spherical aberration</a>. When more magnification or a better image is required, other types of hand magnifier are typically used. A <a href="/facts/Coddington_magnifier/Fdat4opI">Coddington magnifier</a> provides higher magnification with improved image quality. Even better images can be obtained with a multiple-lens magnifier, such as a <a href="/facts/Hastings_triplet/tcCuvt04">Hastings triplet</a>. High power magnifiers are sometimes mounted in a cylindrical or conical holder with no handle, often designed to be worn on the head; this is called a <a href="/facts/Loupe/2H96jv4C">loupe</a>. </p><p>Such magnifiers can reach up to about 30×, and at these magnifications the aperture of the magnifier becomes very small and it must be placed very close to both the object and the eye. For more convenient use or for magnification beyond about 30×, a <a href="/facts/Microscope/ldJp0CI3">microscope</a> is necessary. </p> <p>A <i>sheet magnifier</i> comprises many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner. This arrangement is known as a <a href="/facts/Fresnel_lens/WYbDj3sn">Fresnel lens</a>. Fresnel lenses are used as magnifiers, for example for reading printed text. </p> <h2 id="use-as-a-symbol">Use as a symbol</h2> <p>The magnifying glass (, or U+1F50D in <a href="/facts/Unicode/DDu3MfPV">Unicode</a>: 🔍) is commonly used as a symbolic representation for the ability to search or zoom, especially in computer software and websites.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a><a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> U+1F50E is a right-pointing version: 🔎. </p> <h2 id="see-also">See also</h2> Wikimedia Commons has media related to Magnifying glasses. <ul><li><a href="/facts/Aspheric_lens/cSatFMFd">Aspheric lens</a></li> <li><a href="/facts/Binoculars/DPHVmKIL">Binoculars</a></li> <li><a href="/facts/Burning_glass/uPp2qwxs">Burning glass</a> – Convex lens for fire making</li> <li><a href="/facts/Dome_magnifier/8WT2oxfr">Dome magnifier</a></li> <li><a href="/facts/Glasses/ER3sFKmJ">Glasses</a> – Form of vision aid</li> <li><a href="/facts/Graphoscope/PWhhg77R">Graphoscope</a> – 19th-century magnifying device</li> <li><a href="/facts/Macro_photography/sPKYgzQl">Macro photography</a> – Photography genre and techniques of extreme close-up pictures</li> <li><a href="/facts/Optical_microscope/5700vcna">Optical microscope</a></li> <li><a href="/facts/Optical_telescope/dVfBR10I">Optical telescope</a></li> <li><a href="/facts/Reading_stone/0k9EL5z8">Reading stone</a> – Optical device</li> <li><a href="/facts/Screen_magnifier/6392AGhf">Screen magnifier</a> – Software that enlarges image on part of a computer screen</li> <li><a href="/facts/Stanhope_lens/anrzkWju">Stanhope lens</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Pliny the Elder, Natural History, 36.67, 37.10. <a href="/wiki/Natural_History_(Pliny)" target="_blank">/wiki/Natural_History_(Pliny)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X. <a href="0-201-11609-X" target="_blank">0-201-11609-X</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X. <a href="0-201-11609-X" target="_blank">0-201-11609-X</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X. <a href="0-201-11609-X" target="_blank">0-201-11609-X</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Sines, George; Sakellarakis, Yannis A. (Apr 1987). "Lenses in Antiquity". American Journal of Archaeology. 91 (2): 191–6. doi:10.2307/505216. JSTOR 505216. S2CID 191384703. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Sines, George; Sakellarakis, Yannis A. (1987). "Lenses in Antiquity". American Journal of Archaeology. 91 (2): 191–196. doi:10.2307/505216. ISSN 0002-9114. <a href="https://www.jstor.org/stable/505216" target="_blank">https://www.jstor.org/stable/505216</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Aristophanes, The Clouds, 765–70. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Pliny the Elder, Natural History, 36.67, 37.10. <a href="/wiki/Natural_History_(Pliny)" target="_blank">/wiki/Natural_History_(Pliny)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Seneca, Natural Questions, 1.6.5–7. <a href="/wiki/Naturales_quaestiones" target="_blank">/wiki/Naturales_quaestiones</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>The history of the telescope by Henry C. King, Harold Spencer Jones Publisher Courier Dover Publications, 2003 Pg 25 ISBN 0-486-43265-3, ISBN 978-0-486-43265-6 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Kriss, Timothy C.; Kriss, Vesna Martich (April 1998). "History of the Operating Microscope: From Magnifying Glass to Micro neurosurgery". Neurosurgery. 42 (4): 899–907. doi:10.1097/00006123-199804000-00116. PMID 9574655. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Kriss, Timothy C.; Kriss, Vesna Martich (April 1998). "History of the Operating Microscope: From Magnifying Glass to Micro neurosurgery". Neurosurgery. 42 (4): 899–907. doi:10.1097/00006123-199804000-00116. PMID 9574655. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Amsel-Arieli, M. (2014). Magnifying Glass. History Magazine, 16(1), 6–7. <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"What are all the symbols used by computers?". Computer Hope. Jan 24, 2018. Archived from the original on 2019-04-01. Retrieved 2019-04-01. <a href="https://www.computerhope.com/issues/ch001801.htm" target="_blank">https://www.computerhope.com/issues/ch001801.htm</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Harley, Aurora (July 27, 2014). "Icon Usability". Nielsen Norman Group. Archived from the original on 2019-04-01. Retrieved 2019-04-01. <a href="https://www.nngroup.com/articles/icon-usability/" target="_blank">https://www.nngroup.com/articles/icon-usability/</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> </ol>