Magnifying glass

Magnifying glass
The stamp is under the examination of a magnifying glass
A basic magnifying glass made out of plastic

A magnifying glass (called a hand lens in laboratory contexts) is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle (see image).

A sheet magnifier consists of 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 Fresnel lens.

The magnifying glass is an icon of detective fiction, particularly that of Sherlock Holmes.

Contents

History

The earliest evidence of "a magnifying device, a hi lens forming a magnified image," dates back to 424 BC Aristophanes "lens" is a glass globe filled with water.(Seneca says that it can be used to read letters no matter how small or dim),[1] Roger Bacon described the properties of magnifying glass in 13th-century England, followed by the development of eyeglasses in 13th-century Italy.[2]

Magnification

Magnifying glass on an arm lamp

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.[3] For the "without" case, it is typically assumed that the user would bring the object as close to the eye as possible without it becoming blurry. This point, known as the near point, 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 the eye as long as there are multiple eye pieces in series as one tube and so 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 MP0=¼Φ+1, where Φ is the optical power in dioptres, and the factor of ¼ comes from the assumed distance to the near point (about ¼ m from the eye). This value of the magnifying power is the one normally used to characterize magnifiers. It is typically denoted "m×", where m=MP0. This is sometimes called the total power of the magnifier (again, not to be confused with optical power). The eye moves farther away from the magnifying diamond/glass len is higher magnification but prefer method is adjustment the magnifier in distance variable height between the object/stamp and the glass len.

Magnifiers are not always used as described above, however. It is much 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 MP=¼Φ.

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.

Using this principle, a magnifying glass can also be used to focus light, such as to concentrate the sun's radiation to create a hotspot at the focus point.This is often dangerous for your eyes.

See also

References

  1. ^ The history of the telescope by Henry C. King, Harold Spencer Jones Publisher Courier Dover Publications, 2003 Pg 25 ISBN 0486432653, 9780486432656
  2. ^ 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 
  3. ^ Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X. 

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Look at other dictionaries:

  • magnifying glass — n. A single convex lens which magnifies the apparent dimensions of objects seen through it, and is used to produce an enlarged image. Syn: hand glass. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • magnifying glass — magnifying glasses N COUNT A magnifying glass is a piece of glass which makes objects appear bigger than they actually are …   English dictionary

  • magnifying glass — magnifying .glass n a round piece of glass with a handle, used to make objects or print look bigger …   Dictionary of contemporary English

  • magnifying glass — ► NOUN ▪ a lens that produces an enlarged image, used to examine small or finely detailed things …   English terms dictionary

  • magnifying glass — n. a lens or combination of lenses that increases the apparent size of an object seen through it …   English World dictionary

  • magnifying glass — noun light microscope consisting of a single convex lens that is used to produce an enlarged image (Freq. 1) the magnifying glass was invented by Roger Bacon in 1250 • Syn: ↑hand glass, ↑simple microscope • Hypernyms: ↑light microscope …   Useful english dictionary

  • magnifying glass — UK / US noun [countable] Word forms magnifying glass : singular magnifying glass plural magnifying glasses a small circle of glass, usually with a handle, that makes things appear bigger when you look at them through it …   English dictionary

  • magnifying glass — lupa statusas T sritis Standartizacija ir metrologija apibrėžtis Optinis įtaisas mažiems daiktams įžiūrėti, stebėti ir matuoti. atitikmenys: angl. loupe; magnifying glass; magnifying lens vok. Lupe, f; Vergrößerungslinse, f rus. лупа, f pranc.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • magnifying glass — didinamasis stiklas statusas T sritis fizika atitikmenys: angl. magnifying glass vok. Vergrößerungsglas, n; Vergrößerungslinse, f rus. увеличительное стекло, n pranc. verre grossissant, m …   Fizikos terminų žodynas

  • magnifying glass — Synonyms and related words: achromatic lens, astigmatic lens, burning glass, camera, coated lens, concave lens, concavo convex lens, condenser, convex lens, eyeglass, eyepiece, glass, hand lens, lens, magnifier, meniscus, object glass, objective …   Moby Thesaurus

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