magnifying glass

{{See also|Burning glass}}

A sheet magnifier comprises many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner. The convex lens of a magnifying glass can be used to produce a magnified image 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 focus for fire starting.Pliny the Elder, Natural History, 36.67, 37.10.

=== Magnification ===

{{Main|Magnification}}

File:US Navy 030903-N-2143T-001 Aviation Structural Mechanic Airman John Watkins uses a magnifying glass to check for defects.jpg

The magnification 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 magnifying power is equivalent to angular magnification (this should not be confused with optical power, 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.{{cite book

|first=Eugene

|last=Hecht

|year=1987

|title=Optics

|edition=2nd

|publisher=Addison Wesley

|isbn=0-201-11609-X

|pages=186–188}} 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 near point of accommodation, 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.

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 focus. The object will then typically also be close to the lens. The magnifying power obtained in this condition is {{math|1=MP₀ = d_oΦ + 1}}, where {{mvar|Φ}} is the optical power in dioptres and {{math|d_o}} is the near point of the eye, which is typically assumed to be 0.25 m. This value of the magnifying power is the one normally used to characterize magnifiers. It is typically denoted "{{math|m×"}}, where {{math|1=m = MP₀}}. This is sometimes called the total power of the magnifier (not to be confused with optical power).

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 {{math|1=MP = d_oΦ}}.

A typical magnifying glass might have a focal length 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.

File:Magnification power of a loupe.png

The earliest explicit written evidence of a magnifying device is a joke in Aristophanes's The CloudsAristophanes, The Clouds, 765–70. from 424 BC, where magnifying lenses to ignite tinder were sold in a pharmacy, and Pliny the Elder's "lens", a glass globe filled with water, used to cauterize wounds. Seneca wrote that it could be used to read letters "no matter how small or dim".Seneca, Natural Questions, 1.6.5–7.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}} Over several millennia{{Which?|date=April 2025}} throughout the Middle East and the Mediterranean basin, lenses had widespread use.{{cite journal |last1=Sines |first1=George |last2=Sakellarakis |first2=Yannis A. |date=Apr 1987 |title=Lenses in Antiquity |journal=American Journal of Archaeology |volume=91 |issue=2 |pages=191–6 |doi=10.2307/505216 |jstor=505216 |s2cid=191384703}} Archaeological findings from the 1980s in Crete's Idaean Cave unearthed rock crystal lenses dating back to the Archaic Greek period, 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 antiquity.{{Cite journal |last=Sines |first=George |last2=Sakellarakis |first2=Yannis A. |date=1987 |title=Lenses in Antiquity |url=https://www.jstor.org/stable/505216 |journal=American Journal of Archaeology |volume=91 |issue=2 |pages=191–196 |doi=10.2307/505216 |issn=0002-9114}}

A convex lens used for forming a magnified image was described in the Book of Optics by Ibn al-Haytham in 1021.{{Cite journal |last1=Kriss |first1=Timothy C. |last2=Kriss |first2=Vesna Martich |date=April 1998 |title=History of the Operating Microscope: From Magnifying Glass to Micro neurosurgery |journal=Neurosurgery |volume=42 |issue=4 |pages=899–907 |doi=10.1097/00006123-199804000-00116 |pmid=9574655}}{{Verify source|date=November 2018}} After the book was translated during the Latin translations of the 12th century, Roger Bacon described the properties of a magnifying glass in 13th-century England. This was followed by the development of eyeglasses in 13th-century Italy. In the late 1500s, two Dutch spectacle makers Jacob Metius and Zacharias Janssen crafted the compound microscope by assembling several magnifying lenses in a tube. Hans Lipperhey introduced the telescope in 1608 and Galileo Galilei improved on the device in 1609.Amsel-Arieli, M. (2014). Magnifying Glass. History Magazine, 16(1), 6–7.

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 optical aberrations, particularly spherical aberration. When more magnification or a better image is required, other types of hand magnifier are typically used. A Coddington magnifier provides higher magnification with improved image quality. Even better images can be obtained with a multiple-lens magnifier, such as a Hastings triplet. 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 loupe.

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 microscope is necessary.

A sheet magnifier comprises many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner.{{Citation needed|date=April 2025}} This arrangement is known as a Fresnel lens. Fresnel lenses are used as magnifiers, for example for reading printed text.

The magnifying glass (12px, or U+1F50D in Unicode: 🔍) is commonly used as a symbolic representation for the ability to search or zoom, especially in computer software and websites.{{cite web |url=https://www.computerhope.com/issues/ch001801.htm |title=What are all the symbols used by computers? |website=Computer Hope |date=Jan 24, 2018 |access-date=2019-04-01 |archive-date=2019-04-01 |archive-url=https://web.archive.org/web/20190401051731/https://www.computerhope.com/issues/ch001801.htm |url-status=live }}{{cite web |url=https://www.nngroup.com/articles/icon-usability/ |title=Icon Usability |first=Aurora |last=Harley |date=July 27, 2014 |publisher=Nielsen Norman Group |access-date=2019-04-01 |archive-date=2019-04-01 |archive-url=https://web.archive.org/web/20190401051730/https://www.nngroup.com/articles/icon-usability/ |url-status=live }} U+1F50E is a right-pointing version: 🔎.

{{Commons category|Magnifying glasses}}

• Aspheric lens
• Binoculars
• {{annotated link|Burning glass}}
• {{annotated link|Dome magnifier}}
• {{annotated link|Glasses}}
• {{annotated link|Graphoscope}}
• {{annotated link|Macro photography}}
• Optical microscope
• Optical telescope
• {{annotated link|Reading stone}}
• {{annotated link|Screen magnifier}}
• {{annotated link|Stanhope lens}}

{{Reflist}}

{{Authority control}}

{{DEFAULTSORT:Magnifying Glass}}

Category:Magnifiers

Category:English inventions