Magnifying glass

Last updated April 07, 2024

A magnifying glass 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. Beyond its primary function of magnification, this simple yet ingenious tool serves a variety of purposes. It can be employed to focus sunlight, harnessing the Sun's rays to create a concentrated hot spot at the lens's focus, which is often used for starting fires.

In another innovative form, the magnifying glass can manifest as a sheet magnifier, employing numerous slender, concentric, ring-shaped lenses. These are collectively known as a Fresnel lens, which, despite being significantly thinner, operates effectively as a single lens. This particular design finds its utility in applications such as screen magnifiers for TVs, offering a lightweight and efficient solution for enlarging visuals.

A plastic Fresnel lens sold as a TV-screen magnifier Magnifying-fresnel-lens.jpg — A plastic Fresnel lens sold as a TV-screen magnifier

The cultural impact of the magnifying glass extends far into the realms of literature and pop culture, symbolizing the pursuit of truth and the uncovering of secrets. It is famously associated with the investigative work of fictional detectives, with Sherlock Holmes being the most iconic figure to wield it, cementing its status as an emblem of detective fiction. Through its various forms and functions, the magnifying glass remains a tool of both practical utility and significant symbolic value.

Plural: magnifying glasses

History

"The evidence indicates that the use of lenses was widespread throughout the Middle East and the Mediterranean basin over several millennia".^[1] 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.^[2] The earliest explicit written evidence of a magnifying device is a joke in Aristophanes's The Clouds ^[3] from 424 BC, where magnifying lenses to ignite tinder were sold in a pharmacy, and Pliny the Elder's "lens",^[4] 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".^[5]^[6]) A convex lens used for forming a magnified image was described in the Book of Optics by Ibn al-Haytham in 1021.^[7]^{[ verification needed ]} 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.^[7] Building on this foundation, 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, marking a significant advancement in optical instruments. Not long after, Hans Lipperhey introduced the telescope in 1608 and Galileo Galilei improving on the device in 1609, employing the magnifying lens in an innovative manner, further extending the application of optical technologies developed through the ages.^[8]

Magnification

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.^[9] 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.

A magnifying glass operates as the simplest form of optical instrument. It is essentially a hand-held lens that converges light to produce an enlarged, upright image that appears to stand where light doesn't actually converge, known as a 'virtual' image. To view an item in greater detail, it is positioned between the lens and its focal point, and the optimal observation occurs when the image is at the closest distance at which the eye can focus comfortably. The lens's magnification is the ratio of the image's apparent height to the object's actual height, correlating to the proportion of the distances from the image to the lens and the object to the lens. Moving the object nearer to the lens amplifies this effect, increasing magnification.^[10]

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 MP₀ = (0.25 m)Φ + 1, where Φ is the optical power in dioptres, and the factor of 0.25 m represents the assumed near point (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).

However, 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 MP = (0.25 m)Φ.

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.

Practical uses

A magnifying glass can serve as a fire-starting tool in survival situations. Any transparent lens with significant magnifying ability, such as a standard magnifying glass or a jeweler's loupe, can concentrate sunlight to ignite tinder. The technique involves positioning the lens to focus a small, intense spot of light onto the tinder, awaiting ignition with patience. The advantage of this method is the simplicity of the lens and the minimal effort required. However, its effectiveness is contingent upon clear, strong sunlight, which may be inconsistent depending on geographic location and time of year.^[11]

Beyond survival uses, magnifying glasses are invaluable tools for jewelers and hobbyists. Jewelers rely on them to scrutinize the quality and authenticity of precious gems, ensuring accurate evaluations. Hobbyists, from those engaged in sewing and needlework to stamp collectors, depend on magnifying glasses for detailed work, enhancing both precision and enjoyment. This versatility underlines the magnifying glass's enduring utility across a spectrum of activities, from professional assessments to leisure pursuits.^[8]

Advanced digital magnifiers and apps have emerged as modern alternatives to traditional magnifying glasses, offering features such as variable magnification levels, high-contrast modes, and text-to-speech for visually impaired users. These tools not only magnify text and objects but also enhance readability and accessibility, making them invaluable for daily living and educational purposes.^[12]^[13]

Alternatives

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.

Fresnel lenses are used as magnifiers, for example for reading printed text.

Use as a symbol

The magnifying glass icon (🔍), represented by U+1F50D in Unicode, has evolved into a universal symbol for searching and zooming functions in digital interfaces. Originating from its practical use for detailed examination and discovery, it has been adopted by modern computer software and websites to denote tools for users to find information or closely inspect content.^[9]^[10] The right-pointing version, U+1F50E (🔎), continues this theme, often used to initiate searches. The integration of these icons into user interface design reflects the intuitive connection between the physical act of magnifying to see more clearly and the metaphorical act of searching for information in the digital space.^[14]

Beyond its digital symbolization for search functions, the magnifying glass also holds a place in educational symbolism, often representing curiosity, exploration, and the quest for knowledge. Educational institutions and programs frequently use the magnifying glass in logos and materials to emphasize the importance of inquiry and discovery in learning.^[15]

Related Research Articles

In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with the nature of the distortion depending on the type of aberration. Aberration can be defined as a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements.

$<span class="mw-page-title-main">Lens</span> Optical device which transmits and refracts light$

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.

A microscope is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope.

The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light. A system with a shorter focal length bends the rays more sharply, bringing them to a focus in a shorter distance or diverging them more quickly. For the special case of a thin lens in air, a positive focal length is the distance over which initially collimated (parallel) rays are brought to a focus, or alternatively a negative focal length indicates how far in front of the lens a point source must be located to form a collimated beam. For more general optical systems, the focal length has no intuitive meaning; it is simply the inverse of the system's optical power.

Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models.

A dioptre or diopter, symbol dpt, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m⁻¹. It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at 1⁄3 metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge. Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams.

The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microscope and were possibly invented in their present compound form in the 17th century. Basic optical microscopes can be very simple, although many complex designs aim to improve resolution and sample contrast.

A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocular are typically less than half of a pair of binoculars with similar optical properties, making it more portable and also less expensive. This is because binoculars are essentially a pair of monoculars packed together — one for each eye. As a result, monoculars only produce two-dimensional images, while binoculars can use two parallaxed images to produce binocular vision, which allows stereopsis and depth perception.

An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors.

A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. By enlarging part of a screen, people with visual impairments can better see words and images. This type of assistive technology is useful for people with some functional vision; people with visual impairments and little or no functional vision usually use a screen reader.

<span class="mw-page-title-main">Objective (optics)</span> Lens or mirror in optical instruments

In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.

Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a size ratio called optical magnification. When this number is less than one, it refers to a reduction in size, sometimes called de-magnification.

An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through an optical device to observe an object or sample. The objective lens or mirror collects light from an object or sample and brings it to focus creating an image of the object. The eyepiece is placed near the focal point of the objective to magnify this image to the eyes. The amount of magnification depends on the focal length of the eyepiece.

The eye relief of an optical instrument is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye is outside this distance, a reduced field of view will be obtained. The calculation of eye relief is complex, though generally, the higher the magnification and the larger the intended field of view, the shorter the eye relief.

An optical instrument is a device that processes light waves, either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes, telescopes, and cameras.

A loupe is a simple, small magnification device used to see small details more closely. They generally have higher magnification than a magnifying glass, and are designed to be held or worn close to the eye. A loupe does not have an attached handle, and its focusing lens(es) are contained in an opaque cylinder or cone. On some loupes this cylinder folds into an enclosing housing that protects the lenses when not in use.

Video magnifiers are electronic devices that use a camera and a display screen to perform digital magnification of printed materials. The display screen is usually LCD or a similar flat-screen technology, and the device usually includes a lamp to illuminate the source material. Video magnifiers are designed to be mostly used by people with low vision that cannot be helped using a conventional magnifying glass.

The stereo, stereoscopic or dissecting microscope is an optical microscope variant designed for low magnification observation of a sample, typically using light reflected from the surface of an object rather than transmitted through it. The instrument uses two separate optical paths with two objectives and eyepieces to provide slightly different viewing angles to the left and right eyes. This arrangement produces a three-dimensional visualization of the sample being examined. Stereomicroscopy overlaps macrophotography for recording and examining solid samples with complex surface topography, where a three-dimensional view is needed for analyzing the detail.

The unilens monocular is a simple refracting telescope for field use, designed by Robert Baden-Powell. Consisting of only one lens, it is the simplest of all telescopes, and while occupying very little space can still magnify a distant image up to about four times. The nature of its operation however does not accommodate to everyone's visual acuity, with only three out of four people being able to use it.

A sight magnifier is an optical telescope that can be paired with a non-magnifying optical sight on a weapon to create a telescopic sight. They work with the parallel collimated reticle image produced by red dot sights and holographic weapon sights. They may synonymously be referred to as a red dot magnifier, reflex sight magnifier, holographic sight magnifier, or flip to side magnifiers.

References

↑ 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.
↑ Sines, George; Sakellarakis, Yannis A. (1987). "Lenses in Antiquity". American Journal of Archaeology. 91 (2): 191–196. doi:10.2307/505216. ISSN 0002-9114.
↑ Aristophanes, The Clouds, 765–70.
↑ Pliny the Elder, Natural History, 36.67, 37.10.
↑ 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
1 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.
1 2 Amsel-Arieli, M. (2014). Magnifying Glass. History Magazine, 16(1), 6–7.
1 2 Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X.
1 2 "magnifying glass". search.credoreference.com. Retrieved 2024-03-08.
↑ Williams, J. (2017). FIRE-STARTING TOOLS for Any Situation. Mother Earth News, 281, 67–72.
↑ "30 Apps, Devices and Technologies for People With Vision Impairments". American Academy of Ophthalmology. 2020-08-14. Retrieved 2024-03-10.
↑ "15 BEST DIGITAL MAGNIFIERS FOR THE VISUALLY IMPAIRED | UK | March 2024". UK Care Guide. 2023-08-30. Retrieved 2024-03-10.
↑ "U+1F50E RIGHT-POINTING MAGNIFYING GLASS: 🔎 – Unicode". Codepoints.net. Retrieved 2024-03-09.
↑ Sweeney, Susan Elizabeth (2003). "The Magnifying Glass: Spectacular Distance in Poe's "Man of the Crowd" and Beyond". Poe Studies. 36 (1): 3–17. ISSN 1754-6095.

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[1] 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.

[2] Sines, George; Sakellarakis, Yannis A. (1987). "Lenses in Antiquity". American Journal of Archaeology. 91 (2): 191–196. doi:10.2307/505216. ISSN 0002-9114.

[3] Aristophanes, The Clouds, 765–70.

[4] Pliny the Elder, Natural History, 36.67, 37.10.

[5] Seneca, Natural Questions, 1.6.5–7.

[6] 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

[Kriss-7] 1 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.

[:0-8] 1 2 Amsel-Arieli, M. (2014). Magnifying Glass. History Magazine, 16(1), 6–7.

[:1-9] 1 2 Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. pp. 186–188. ISBN 0-201-11609-X.

[:2-10] 1 2 "magnifying glass". search.credoreference.com. Retrieved 2024-03-08.

[11] Williams, J. (2017). FIRE-STARTING TOOLS for Any Situation. Mother Earth News, 281, 67–72.

[12] "30 Apps, Devices and Technologies for People With Vision Impairments". American Academy of Ophthalmology. 2020-08-14. Retrieved 2024-03-10.

[13] "15 BEST DIGITAL MAGNIFIERS FOR THE VISUALLY IMPAIRED | UK | March 2024". UK Care Guide. 2023-08-30. Retrieved 2024-03-10.

[14] "U+1F50E RIGHT-POINTING MAGNIFYING GLASS: 🔎 – Unicode". Codepoints.net. Retrieved 2024-03-09.

[15] Sweeney, Susan Elizabeth (2003). "The Magnifying Glass: Spectacular Distance in Poe's "Man of the Crowd" and Beyond". Poe Studies. 36 (1): 3–17. ISSN 1754-6095.

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