Editing Optical microscope

{{short description|Microscope that uses visible light}}
{{Use dmy dates|date=March 2019}}

[[File:Scientists are working in the lab.9.jpg|thumb|300px| Scientist using an optical microscope in a laboratory]]

The '''optical microscope''', also referred to as a '''light microscope''', is a type of [[microscope]] that commonly uses [[visible spectrum|visible light]] and a system of [[lens (optics)|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 [[optical resolution|resolution]] and sample [[contrast (vision)|contrast]].{{Citation needed|date=August 2024}}

The object is placed on a '''stage''' and may be directly viewed through one or two [[eyepiece]]s on the microscope. In high-power microscopes, both eyepieces typically show the same image, but with a [[stereo microscope]], slightly different images are used to create a 3-D effect. A camera is typically used to capture the image ([[micrograph]]).{{Citation needed|date=August 2024}}

The sample can be lit in a variety of ways. Transparent objects can be lit from below and solid objects can be lit with light coming through ([[Bright-field microscopy|bright field]]) or around ([[Dark-field microscopy|dark field]]) the objective lens. [[Polarised light]] may be used to determine crystal orientation of metallic objects. [[Phase-contrast imaging]] can be used to increase image contrast by highlighting small details of differing refractive index.{{Citation needed|date=August 2024}}

A range of [[Objective (optics)|objective]] lenses with different magnification are usually provided mounted on a turret, allowing them to be rotated into place and providing an ability to zoom-in. The maximum magnification power of optical microscopes is typically limited to around 1000x because of the limited resolving power of visible light. While larger magnifications are possible no additional details of the object are resolved.{{Citation needed|date=August 2024}}

Alternatives to optical microscopy which do not use visible light include [[scanning electron microscopy]] and [[transmission electron microscopy]] and [[scanning probe microscopy]] and as a result, can achieve much greater magnifications.

==Types==
[[File:Microscope simple diagram.png|thumb|right|150px|Diagram of a simple microscope]]
There are two basic types of optical microscopes: simple microscopes and compound microscopes. A simple microscope uses the [[optical power]] of a single lens or group of lenses for magnification. A compound microscope uses a system of lenses (one set enlarging the image produced by another) to achieve a much higher magnification of an object. The vast majority of modern [[research]] microscopes are compound microscopes, while some cheaper commercial [[digital microscope]]s are simple single-lens microscopes. Compound microscopes can be further divided into a variety of other types of microscopes, which differ in their optical configurations, cost, and intended purposes.{{Citation needed|date=August 2024}}

===Simple microscope===
A simple microscope uses a lens or set of lenses to enlarge an object through angular magnification alone, giving the viewer an erect enlarged [[virtual image]].<ref>{{cite web |url=http://www.msnucleus.org/membership/html/jh/biological/microscopes/lesson2/microscopes2c.html |publisher=msnucleus.org |access-date=15 January 2017 |title=Lesson 2 – Page 3, CLASSIFICATION OF MICROSCOPES |author=JR Blueford |url-status=live |archive-url=https://web.archive.org/web/20160510210018/http://msnucleus.org/membership/html/jh/biological/microscopes/lesson2/microscopes2c.html |archive-date=10 May 2016  }}</ref><ref>{{cite book|author=Trisha Knowledge Systems|title=The IIT Foundation Series - Physics Class 8, 2/e|url=https://books.google.com/books?id=NKh9dQKnTdEC&pg=PA213|publisher=Pearson Education India|isbn=978-81-317-6147-2|page=213}}</ref> The use of a single convex lens or groups of lenses are found in simple magnification devices such as the [[magnifying glass]], [[loupe]]s, and [[eyepiece]]s for [[telescope]]s and microscopes.{{cn|date=December 2024}}

===Compound microscope===
[[File:Compound microscope geometric optics.svg|thumb|left|400px|Ray optics diagram of a compound microscope.]]

A compound microscope uses a lens close to the object being viewed to collect light (called the [[Objective (optics)|objective]] lens), which focuses a [[real image]] of the object inside the microscope. That image is then magnified by a second lens or group of lenses (called the [[eyepiece]]) that gives the viewer an enlarged inverted virtual image of the object. <ref name=Watt>{{cite book|author=Ian M. Watt|title=The Principles and Practice of Electron Microscopy|url=https://books.google.com/books?id=Y6-sE4gUX-QC&pg=PA6|year=1997|publisher=Cambridge University Press|isbn=978-0-521-43591-8|page=6}}</ref> 

The use of a compound objective-eyepiece combination allows for much higher angular magnification:
For an object of height <math>h</math>,
it can at most occupy an unmagnified [[angular size]] <math>\theta_0 = h / d_0</math> while remaining in focus,
achieved when it is placed at the [[Near point|near point distance]] <math> d_0 </math> of the eye (about 11 cm).
The virtual image created by the compound microscope achieves an angular size of
<math> \theta = -h s /f_\text{objective}f_\text{eyepiece}</math>,
where <math> s</math> is the distance between the neighboring objective and eyepiece focal points.
This is an angular magnification of <math>\theta/\theta_0 = -s d_0 /f_\text{objective}f_\text{eyepiece}</math>.

Common compound microscopes often feature exchangeable objective lenses, allowing the user to quickly adjust the magnification.<ref name=Watt/> A compound microscope also enables more advanced illumination setups, such as [[phase contrast]].{{cn|date=December 2024}}

===Other microscope variants===
There are many variants of the compound optical microscope design for specialized purposes. Some of these are physical design differences allowing specialization for certain purposes:{{cn|date=December 2024}}
* [[Stereo microscope]], a low-powered microscope which provides a stereoscopic view of the sample, commonly used for dissection.
* [[Comparison microscope]] has two separate light paths allowing direct comparison of two samples via one image in each eye.
* [[Inverted microscope]], for studying samples from below; useful for cell cultures in liquid or for metallography.
* Fiber optic connector inspection microscope, designed for connector end-face inspection
* [[Traveling microscope]], for studying samples of high [[optical resolution]].

Other microscope variants are designed for different illumination techniques:
* [[Petrographic microscope]], whose design usually includes a polarizing filter, rotating stage, and gypsum plate to facilitate the study of minerals or other crystalline materials whose optical properties can vary with orientation.
* [[Polarizing microscope]], similar to the petrographic microscope.
* [[Phase-contrast microscope]], which applies the phase contrast illumination method.
* [[Epifluorescence microscope]], designed for analysis of samples that include fluorophores.
* [[Confocal microscope]], a widely used variant of epifluorescent illumination that uses a scanning laser to illuminate a sample for fluorescence.
* [[Two-photon excitation microscopy|Two-photon microscope]], used to image fluorescence deeper in scattering media and reduce photobleaching, especially in living samples.
* Student microscope – an often low-power microscope with simplified controls and sometimes low-quality optics designed for school use or as a starter instrument for children.<ref>{{cite web|url=http://www.well.ox.ac.uk/_asset/file/buying-a-cheap-microscope-for-home.pdf|title=Buying a cheap microscope for home use|access-date=5 November 2015|publisher=Oxford University.|url-status=live|archive-url=https://web.archive.org/web/20160305042314/http://www.well.ox.ac.uk/_asset/file/buying-a-cheap-microscope-for-home.pdf|archive-date=5 March 2016}}</ref>
* [[Ultramicroscope]], an adapted light microscope that uses [[light scattering]] to allow viewing of tiny particles whose diameter is below or near the wavelength of visible light (around 500 nanometers); mostly obsolete since the advent of [[electron microscope]]s
* [[Tip-enhanced Raman spectroscopy|Tip-enhanced Raman microscope]], is a variant of optical microscope based on [[tip-enhanced Raman spectroscopy]], without traditional wavelength-based resolution limits.<ref>{{Cite journal|last1=Kumar|first1=Naresh|last2=Weckhuysen|first2=Bert M.|last3=Wain|first3=Andrew J.|last4=Pollard|first4=Andrew J.|date=April 2019|title=Nanoscale chemical imaging using tip-enhanced Raman spectroscopy|journal=Nature Protocols|volume=14|issue=4|pages=1169–1193|doi=10.1038/s41596-019-0132-z|pmid=30911174|issn=1750-2799|doi-access=free}}</ref><ref>{{Cite journal|last1=Lee|first1=Joonhee|last2=Crampton|first2=Kevin T.|last3=Tallarida|first3=Nicholas|last4=Apkarian|first4=V. Ara|date=April 2019|title=Visualizing vibrational normal modes of a single molecule with atomically confined light|journal=Nature|volume=568|issue=7750|pages=78–82|doi=10.1038/s41586-019-1059-9|pmid=30944493|bibcode=2019Natur.568...78L |s2cid=92998248 |issn=1476-4687}}</ref> This microscope primarily realized on the [[Scanning probe microscopy|scanning-probe microscope]] platforms using all optical tools.

===Digital microscope===
[[File:2008Computex DnI Award AnMo Dino-Lite Digital Microscope.jpg|thumb|right|200px|A miniature [[USB microscope]]]]
{{Main|Digital microscope}}
A digital microscope is a microscope equipped with a [[digital camera]] allowing observation of a sample via a [[computer]]. Microscopes can also be partly or wholly computer-controlled with various levels of automation. Digital microscopy allows greater analysis of a microscope image, for example, measurements of distances and areas and quantitation of a fluorescent or [[histology|histological]] stain.{{cn|date=December 2024}}

Low-powered digital microscopes, [[USB microscope]]s, are also commercially available. These are essentially [[webcam]]s with a high-powered [[macro lens]] and generally do not use [[transillumination]]. The camera is attached directly to a computer's [[USB]] port to show the images directly on the monitor. They offer modest magnifications (up to about 200×) without the need to use eyepieces and at a very low cost. High-power illumination is usually provided by an [[LED]] source or sources adjacent to the camera lens.{{cn|date=December 2024}}

Digital microscopy with very low light levels to avoid damage to vulnerable biological samples is available using sensitive [[photon counting|photon-counting]] digital cameras. It has been demonstrated that a light source providing pairs of [[Photon entanglement|entangled photons]] may minimize the risk of damage to the most light-sensitive samples. In this application of [[ghost imaging]] to photon-sparse microscopy, the sample is illuminated with infrared photons, each spatially correlated with an entangled partner in the visible band for efficient imaging by a photon-counting camera.<ref name="AspdenGemmell2015">{{cite journal|last1=Aspden|first1=Reuben S. |last2=Gemmell|first2=Nathan R. |last3=Morris|first3=Peter A. |last4=Tasca|first4=Daniel S. |last5=Mertens|first5=Lena |last6=Tanner|first6=Michael G. |last7=Kirkwood|first7=Robert A. |last8=Ruggeri|first8=Alessandro |last9=Tosi|first9=Alberto |last10=Boyd|first10=Robert W. |last11=Buller|first11=Gerald S. |last12=Hadfield |first12=Robert H. |last13=Padgett |first13=Miles J. |title=Photon-sparse microscopy: visible light imaging using infrared illumination |journal=Optica |volume=2 |issue=12 |year=2015 |pages=1049 |issn=2334-2536 |doi=10.1364/OPTICA.2.001049|bibcode=2015Optic...2.1049A |url=http://eprints.gla.ac.uk/112219/1/112219.pdf |archive-url=https://web.archive.org/web/20160604104215/http://eprints.gla.ac.uk/112219/1/112219.pdf |archive-date=2016-06-04 |url-status=live |doi-access=free }}</ref>

==History==
{{See also|History of optics|Timeline of microscope technology}}

===Invention===
The earliest microscopes were single [[lens (optics)|lens]] [[magnifying glass]]es with limited magnification, which date at least as far back as the widespread use of lenses in [[eyeglasses]] in the 13th century.<ref>Atti Della Fondazione Giorgio Ronchi E Contributi Dell'Istituto Nazionale Di Ottica, Volume 30, La Fondazione-1975, page 554</ref>

Compound microscopes first appeared in Europe around 1620<ref>{{cite book|author1=Albert Van Helden|author2=Sven Dupré|author3=Rob van Gent|title=The Origins of the Telescope|url=https://books.google.com/books?id=XguxYlYd-9EC&pg=PA24|year=2010|publisher=Amsterdam University Press|isbn=978-90-6984-615-6|page=24}}</ref><ref name="J. William Rosenthal 1996, page 391"/> including one demonstrated by [[Cornelis Drebbel]] in London (around 1621) and one exhibited in Rome in 1624.<ref name="Raymond J. Seeger 2016, page 24">Raymond J. Seeger, Men of Physics: Galileo Galilei, His Life and His Works, Elsevier - 2016, page 24</ref><ref name="J. William Rosenthal 1996, page 391">J. William Rosenthal, Spectacles and Other Vision Aids: A History and Guide to Collecting, Norman Publishing, 1996, page 391–2</ref>

The actual inventor of the compound microscope is unknown although many claims have been made over the years. These include a claim 35<ref>{{cite book|author1=Albert Van Helden|author2=Sven Dupré|author3=Rob van Gent|title=The Origins of the Telescope|url=https://books.google.com/books?id=XguxYlYd-9EC&pg=PA36|year=2010|publisher=Amsterdam University Press|isbn=978-90-6984-615-6|pages=32–36, 43}}</ref> years after they appeared by [[Dutch people|Dutch]] spectacle-maker Johannes Zachariassen that his father, [[Zacharias Janssen]], invented the compound microscope and/or the telescope as early as 1590. Johannes' testimony, which some claim is dubious,<ref>[[#Van Helden|Van Helden]], p. 43</ref><ref name=Shmaefsky>Shmaefsky, Brian (2006) ''Biotechnology 101''. Greenwood. p. 171. {{ISBN|0313335281}}.</ref><ref>Note: stories vary, including Zacharias Janssen had the help of his father Hans Martens (or sometimes said to have been built entirely by his father). Zacharias' probable birth date of 1585 ([[#Van Helden|Van Helden]], p. 28) makes it unlikely he invented it in 1590 and the claim of invention is based on the testimony of Zacharias Janssen's son, Johannes Zachariassen, who may have fabricated the whole story ([[#Van Helden|Van Helden]], p. 43).</ref> pushes the invention date so far back that Zacharias would have been a child at the time, leading to speculation that, for Johannes' claim to be true, the compound microscope would have to have been invented by Johannes' grandfather, Hans Martens.<ref name=Shmaefsky/> Another claim is that Janssen's competitor, [[Hans Lippershey]] (who applied for the first telescope patent in 1608) also invented the compound microscope.<ref>{{cite web|url=http://www.livescience.com/39649-who-invented-the-microscope.html|title=Who Invented the Microscope?|website=[[Live Science]] |date=14 September 2013 |access-date=31 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170203052525/http://www.livescience.com/39649-who-invented-the-microscope.html|archive-date=3 February 2017}}</ref> Other historians point to the Dutch innovator Cornelis Drebbel with his 1621 compound microscope.<ref name="Raymond J. Seeger 2016, page 24"/><ref name="J. William Rosenthal 1996, page 391"/>

[[Galileo Galilei]] is sometimes cited as a compound microscope inventor. After 1610, he found that he could close focus his telescope to view small objects, such as flies, close up<ref>Robert D. Huerta, Giants of Delft: Johannes Vermeer and the Natural Philosophers : the Parallel Search for Knowledge During the Age of Discovery, Bucknell University Press - 2003, page 126</ref> and/or could look through the wrong end in reverse to magnify small objects.<ref>A. Mark Smith, From Sight to Light: The Passage from Ancient to Modern Optics, University of Chicago Press - 2014, page 387</ref> The only drawback was that his 2 foot long telescope had to be extended out to 6 feet to view objects that close.<ref>Daniel J. Boorstin, The Discoverers, Knopf Doubleday Publishing Group - 2011, page 327</ref> After seeing the compound microscope built by  Drebbel exhibited in Rome in 1624, Galileo built his own improved version.<ref name="Raymond J. Seeger 2016, page 24"/><ref name="J. William Rosenthal 1996, page 391"/> In 1625, [[Giovanni Faber]] coined the name ''microscope'' for the compound microscope Galileo submitted to the {{lang|it|[[Accademia dei Lincei]]|italic=no}} in 1624 <ref>{{cite book |author=Gould, Stephen Jay |title=The Lying Stones of Marrakech: Penultimate Reflections in Natural History |url=https://archive.org/details/isbn_9780095031417 |url-access=registration | chapter = Chapter 2: The Sharp-Eyed Lynx, Outfoxed by Nature |publisher=Harmony |location=New York, N.Y |year=2000 |isbn=978-0-224-05044-9}}</ref> (Galileo had called it the "''occhiolino''" or "''little eye''"). Faber coined the name from the [[Greek language|Greek]] words ''μικρόν'' (micron) meaning "small", and ''σκοπεῖν'' (skopein) meaning "to look at", a name meant to be analogous with "telescope", another word coined by the Linceans.<ref>[http://brunelleschi.imss.fi.it/esplora/microscopio/dswmedia/risorse/testi_completi.pdf "Il microscopio di Galileo"] {{webarchive|url=https://web.archive.org/web/20080409010159/http://brunelleschi.imss.fi.it/esplora/microscopio/dswmedia/risorse/testi_completi.pdf |date=9 April 2008 }}, Instituto e Museo di Storia della Scienza (in Italian)</ref>

[[Christiaan Huygens]], another Dutchman, developed a simple 2-lens ocular system in the late 17th century that was [[Achromatic lens|achromatically]] corrected, and therefore a huge step forward in microscope development. The Huygens ocular is still being produced to this day, but suffers from a small field size, and other minor disadvantages.{{cn|date=December 2024}}

===Popularization===
[[File:Stelluti bees1630.jpg|thumb|right|The oldest published image known to have been made with a microscope: bees by [[Francesco Stelluti]], 1630<ref>Gould, Stephen Jay (2000) ''[[The Lying Stones of Marrakech]]''. Harmony Books. {{ISBN|0-609-60142-3}}.</ref>]]
[[Antonie van Leeuwenhoek]] (1632–1724) is credited with bringing the microscope to the attention of biologists, even though simple magnifying lenses were already being produced in the 16th century. Van Leeuwenhoek's home-made microscopes were simple microscopes, with a single very small, yet strong lens. They were awkward in use, but enabled van Leeuwenhoek to see detailed images. It took about 150 years of optical development before the compound microscope was able to provide the same quality image as van Leeuwenhoek's simple microscopes, due to difficulties in configuring multiple lenses. In the 1850s, [[John Leonard Riddell]], Professor of Chemistry at [[Tulane University]], invented the first practical binocular microscope while carrying out one of the earliest and most extensive American microscopic investigations of [[cholera]].<ref name="Riddell">{{cite journal | author = Riddell JL | title = On the binocular microscope | journal = Q J Microsc Sci | volume = 2 | pages = 18–24 | year = 1854}}</ref><ref name="Cassedy">{{cite journal | author = Cassedy JH | title = John L. Riddell's Vibrio biceps: Two documents on American microscopy and cholera etiology 1849–59 | journal = J Hist Med | volume = 28 | pages = 101–108 | year = 1973 | issue=2| doi = 10.1093/jhmas/xxviii.2.101 | pmid = 4572620 }}</ref>

===Lighting techniques===
While basic microscope technology and optics have been available for over 400 years it is much more recently that techniques in sample illumination were developed to generate the high quality images seen today.{{Citation needed|date=August 2024}}

In August 1893, [[August Köhler]] developed [[Köhler illumination]]. This method of sample illumination gives rise to extremely even lighting and overcomes many limitations of older techniques of sample illumination. Before development of Köhler illumination the image of the light source, for example a [[lightbulb]] filament, was always visible in the image of the sample.{{Citation needed|date=August 2024}}

The [[Nobel Prize]] in physics was awarded to Dutch physicist [[Frits Zernike]] in 1953 for his development of [[phase contrast]] illumination which allows imaging of transparent samples. By using [[Interference (wave propagation)|interference]] rather than [[Absorption (electromagnetic radiation)|absorption]] of light, extremely transparent samples, such as live [[mammalian]] cells, can be imaged without having to use staining techniques. Just two years later, in 1955, [[Georges Nomarski]] published the theory for [[differential interference contrast]] microscopy, another [[Interference (wave propagation)|interference]]-based imaging technique.{{Citation needed|date=August 2024}}

===Fluorescence microscopy===
Modern biological microscopy depends heavily on the development of [[fluorescent]] [[Hybridization probe|probe]]s for specific structures within a cell. In contrast to normal transilluminated light microscopy, in [[fluorescence microscopy]] the sample is illuminated through the objective lens with a narrow set of wavelengths of light. This light interacts with fluorophores in the sample which then emit light of a longer [[wavelength]]. It is this emitted light which makes up the image.{{cn|date=December 2024}}

Since the mid-20th century chemical fluorescent stains, such as [[DAPI]] which binds to [[DNA]], have been used to label specific structures within the cell. More recent developments include [[immunofluorescence]], which uses fluorescently labelled [[antibodies]] to recognise specific proteins within a sample, and fluorescent proteins like [[Green fluorescent protein|GFP]] which a live cell can [[gene expression|express]] making it fluorescent.{{cn|date=December 2024}}

==Components==
[[File:Optical microscope nikon alphaphot.jpg|thumb|right|300px|Basic optical transmission microscope elements (1990s)]]

All modern optical microscopes designed for viewing samples by transmitted light share the same basic components of the light path. In addition, the vast majority of microscopes have the same 'structural' components<ref>{{Cite web|title=How to Use a Compound Microscope|url=https://www.microscope.com/education-center/how-to-guides/how-to-use-a-compound-microscope/|access-date=2023-02-08|website=Microscope.com|language=en}}</ref> (numbered below according to the image on the right):{{cn|date=December 2024}}
* [[Eyepiece]] (ocular lens) (1)
* Objective turret, revolver, or revolving nose piece (to hold multiple objective lenses) (2)
* [[objective (optics)|Objective lenses]] (3)
* Focus knobs (to move the stage)
** Coarse adjustment (4)
** Fine adjustment (5)
* Stage (to hold the specimen) (6)
* Light source (a [[light]] or a [[mirror]]) (7)
* Diaphragm and [[condenser (microscope)|condenser]] (8)
* Mechanical stage (9)

===Eyepiece (ocular lens)===
{{Main|Eyepiece}}

The [[eyepiece]], or ocular lens, is a cylinder containing two or more lenses; its function is to bring the image into focus for the eye. The eyepiece is inserted into the top end of the body tube. Eyepieces are interchangeable and many different eyepieces can be inserted with different degrees of magnification. Typical magnification values for eyepieces include 5×, 10× (the most common), 15× and 20×. In some high performance microscopes, the optical configuration of the objective lens and eyepiece are matched to give the best possible optical performance. This occurs most commonly with [[apochromat]]ic objectives.{{cn|date=December 2024}}

===Objective turret (revolver or revolving nose piece)===
Objective turret, revolver, or revolving nose piece is the part that holds the set of objective lenses. It allows the user to switch between objective lenses.{{cn|date=December 2024}}

===Objective lens===
{{Main|Objective (optics)}}

At the lower end of a typical compound optical microscope, there are one or more [[objective lens]]es that collect light from the sample. The objective is usually in a cylinder housing containing a glass single or multi-element compound lens. Typically there will be around three objective lenses screwed into a circular nose piece which may be rotated to select the required objective lens. These arrangements are designed to be [[Parfocal lens|parfocal]], which means that when one changes from one lens to another on a microscope, the sample stays in [[focus (optics)|focus]]. Microscope objectives are characterized by two parameters, namely, [[magnification]] and [[numerical aperture]]. The former typically ranges from 5× to 100× while the latter ranges from 0.14 to 0.7, corresponding to [[focal length]]s of about 40 to 2&nbsp;mm, respectively. Objective lenses with higher magnifications normally have a higher numerical aperture and a shorter [[depth of field]] in the resulting image. Some high performance objective lenses may require matched eyepieces to deliver the best optical performance.{{cn|date=December 2024}}

====Oil immersion objective====
[[File:Leica EpifluorescenceMicroscope ObjectiveLens.jpg|thumb|right|300px|Two Leica [[oil immersion]] microscope objective lenses: 100× (left) and 40× (right)]]
{{Main|Oil immersion}}

Some microscopes make use of [[oil-immersion objective]]s or water-immersion objectives for greater resolution at high magnification. These are used with [[index-matching material]] such as [[immersion oil]] or water and a matched cover slip between the objective lens and the sample. The refractive index of the index-matching material is higher than air allowing the objective lens to have a larger numerical aperture (greater than 1) so that the light is transmitted from the specimen to the outer face of the objective lens with minimal refraction. Numerical apertures as high as 1.6 can be achieved.<ref>{{cite web |url=http://www.olympusmicro.com/primer/anatomy/objectives.html |title=Microscope objectives |work=Olympus Microscopy Resource Center |first=Spring |last=Kenneth |author2=Keller, H. Ernst |author3=Davidson, Michael W. |access-date=29 October 2008 |url-status=live |archive-url=https://web.archive.org/web/20081101133539/http://www.olympusmicro.com/primer/anatomy/objectives.html |archive-date=1 November 2008  }}</ref> The larger numerical aperture allows collection of more light making detailed observation of smaller details possible. An oil immersion lens usually has a magnification of 40 to 100×.{{cn|date=December 2024}}

===Focus knobs===
Adjustment knobs move the stage up and down with separate adjustment for coarse and fine focusing. The same controls enable the microscope to adjust to specimens of different thickness. In older designs of microscopes, the focus adjustment wheels move the microscope tube up or down relative to the stand and had a fixed stage.{{cn|date=December 2024}}

===Frame===
The whole of the optical assembly is traditionally attached to a rigid arm, which in turn is attached to a robust U-shaped foot to provide the necessary rigidity. The arm angle may be adjustable to allow the viewing angle to be adjusted.{{cn|date=December 2024}}

The frame provides a mounting point for various microscope controls. Normally this will include controls for focusing, typically a large knurled wheel to adjust coarse focus, together with a smaller knurled wheel to control fine focus. Other features may be lamp controls and/or controls for adjusting the condenser.{{cn|date=December 2024}}

===Stage===
The stage is a platform below the objective lens which supports the specimen being viewed. In the center of the stage is a hole through which light passes to illuminate the specimen. The stage usually has arms to hold [[Microscope slide|slides]] (rectangular glass plates with typical dimensions of 25×75&nbsp;mm, on which the specimen is mounted).{{cn|date=December 2024}}

At magnifications higher than 100× moving a slide by hand is not practical. A mechanical stage, typical of medium and higher priced microscopes, allows tiny movements of the slide via control knobs that reposition the sample/slide as desired. If a microscope did not originally have a mechanical stage it may be possible to add one.{{cn|date=December 2024}}

All stages move up and down for focus. With a mechanical stage slides move on two horizontal axes for positioning the specimen to examine specimen details.{{cn|date=December 2024}}

Focusing starts at lower magnification in order to center the specimen by the user on the stage. Moving to a higher magnification requires the stage to be moved higher vertically for re-focus at the higher magnification and may also require slight horizontal specimen position adjustment. Horizontal specimen position adjustments are the reason for having a mechanical stage.{{cn|date=December 2024}}

Due to the difficulty in preparing specimens and mounting them on slides, for children it is best to begin with prepared slides that are centered and focus easily regardless of the focus level used.{{cn|date=December 2024}}

===Light source===
Many sources of light can be used. At its simplest, daylight is directed via a [[mirror]]. Most microscopes, however, have their own adjustable and controllable light source – often a [[halogen lamp]], although illumination using [[LED]]s and [[laser]]s are becoming a more common provision. [[Köhler illumination]] is often provided on more expensive instruments.{{cn|date=December 2024}}

===Condenser===
The [[condenser (microscope)|condenser]] is a lens designed to focus light from the illumination source onto the sample. The condenser may also include other features, such as a [[diaphragm (optics)|diaphragm]] and/or filters, to manage the quality and intensity of the illumination. For illumination techniques like [[dark field]], [[phase contrast]] and [[differential interference contrast]] microscopy additional optical components must be precisely aligned in the light path.{{cn|date=December 2024}}

===Magnification===
The actual power or [[magnification]] of a compound optical microscope is the product of the powers of the [[eyepiece]] and the objective lens. For example a 10x eyepiece magnification and a 100x objective lens magnification gives a total magnification of 1,000×.  Modified environments such as the use of oil or ultraviolet light can increase the resolution and allow for resolved details at magnifications larger than 1,000x.{{cn|date=December 2024}}

==Operation==
[[Image:CBP checking authenticity of a travel document.jpg|thumb|right|250px|U.S. [[U.S. Customs and Border Protection|CBP]] [[Office of Field Operations]] agent checking the [[Authentication|authenticity]] of a [[travel document]] at an [[international airport]] using a [[stereo microscope]]]]

===Illumination techniques===
{{main|Microscopy}}
Many techniques are available which modify the light path to generate an improved [[contrast (vision)|contrast]] image from a sample. Major techniques for generating increased contrast from the sample include [[Polarized light microscopy|cross-polarized light]], [[dark field]], [[phase contrast]] and [[differential interference contrast]] illumination. A recent technique ([[Sarfus]]) combines [[Polarized light microscopy|cross-polarized light]] and specific contrast-enhanced slides for the visualization of nanometric samples.{{cn|date=December 2024}}
<gallery caption="Four examples of transilumination techniques used to generate contrast in a sample of [[tissue paper]]. 1.559 μm/pixel." align="center">
File:Paper Micrograph Bright.png|[[Bright field microscopy|Bright field]] illumination, sample contrast comes from [[absorbance]] of light in the sample.
File:Paper Micrograph Cross-Polarised.png|[[Polarized light microscopy|Cross-polarized light]] illumination, sample contrast comes from rotation of [[Polarization (waves)|polarized]] light through the sample.
File:Paper Micrograph Dark.png|[[Dark field]] illumination, sample contrast comes from light [[scattered radiation|scattered]] by the sample.
File:Paper Micrograph Phase.png|[[Phase contrast]] illumination, sample contrast comes from [[Interference (wave propagation)|interference]] of different path lengths of light through the sample.
</gallery>

===Other techniques===
Modern microscopes allow more than just observation of transmitted light image of a sample; there are many techniques which can be used to extract other kinds of data. Most of these require additional equipment in addition to a basic compound microscope.{{cn|date=December 2024}}
* Reflected light, or incident, illumination (for analysis of surface structures)
* Fluorescence microscopy, both:
:*[[Epifluorescence microscopy]]
:*[[Confocal microscopy]]
* [[Ultraviolet–visible spectroscopy|Microspectroscopy]] (where a UV-visible spectrophotometer is integrated with an optical microscope)
* Ultraviolet microscopy
* Near-Infrared microscopy
* Multiple transmission microscopy<ref>{{Cite journal|last1=Pégard|first1=Nicolas C.|last2=Fleischer|first2=Jason W.|date=2011-05-01|title=Contrast Enhancement by Multi-Pass Phase-Conjugation Microscopy|url=https://opg.optica.org/abstract.cfm?uri=CLEO_SI-2011-CThW6|journal=CLEO:2011 - Laser Applications to Photonic Applications (2011), Paper CThW6|language=EN|publisher=Optica Publishing Group|pages=CThW6|doi=10.1364/CLEO_SI.2011.CThW6|isbn=978-1-55752-910-7 |s2cid=13366261 |url-access=subscription}}</ref> for contrast enhancement and aberration reduction.
* Automation (for automatic scanning of a large sample or image capture)

==Applications==
[[File:Vaginal wet mount of candidal vulvovaginitis.jpg|thumb| A 40x magnification image of cells in a medical [[smear test]] taken through an optical microscope using a [[wet mount]] technique, placing the specimen on a glass slide and mixing with a salt solution]]
Optical microscopy is used extensively in microelectronics, nanophysics, biotechnology, pharmaceutic research, mineralogy and microbiology.<ref>[http://www.fy.chalmers.se/microscopy/students/imagecourse/O1.pdf O1 Optical Microscopy] {{Webarchive|url=https://web.archive.org/web/20110124110445/http://www.fy.chalmers.se/microscopy/students/imagecourse/O1.pdf |date=24 January 2011 }} By Katarina Logg. Chalmers Dept. Applied Physics. 20 January 2006</ref>

Optical microscopy is used for [[medical diagnosis]], the field being termed [[histopathology]] when dealing with tissues, or in [[smear test]]s on free cells or tissue fragments.{{cn|date=December 2024}}

In industrial use, binocular microscopes are common. Aside from applications needing true [[Stereo microscope|depth perception]], the use of dual eyepieces reduces [[Asthenopia|eye strain]] associated with long workdays at a microscopy station. In certain applications, long-working-distance or long-focus microscopes<ref name="macrolensdb">{{cite web | url=http://www.macrolenses.de/ml_detail_sl.php?ObjektiveNr=315 | title=Long-focus microscope with camera adapter | work=macrolenses.de | url-status=live | archive-url=https://web.archive.org/web/20111003192049/http://www.macrolenses.de/ml_detail_sl.php?ObjektiveNr=315 | archive-date=3 October 2011 | df=dmy-all }}</ref> are beneficial.  An item may need to be examined behind a [[Optical window|window]], or industrial subjects may be a hazard to the objective.  Such optics resemble telescopes with close-focus capabilities.<ref name="questar">{{cite web | url=http://company7.com/questar/microscope.html/ | title=Questar Maksutov microscope | work=company7.com | url-status=dead | archive-url=https://web.archive.org/web/20110615194516/http://www.company7.com/questar/microscope.html | archive-date=15 June 2011 | df=dmy-all | access-date=11 July 2011 }}</ref><ref name="fta">{{cite web| url=http://www.firsttenangstroms.com/accessories/longrangemicroscope/LongRangeMicroscope.html/| work=firsttenangstroms.com| title=FTA long-focus microscope| url-status=dead| archive-url=https://web.archive.org/web/20120226020029/http://www.firsttenangstroms.com/accessories/longrangemicroscope/LongRangeMicroscope.html| archive-date=26 February 2012| df=dmy-all| access-date=11 July 2011}}</ref>

Measuring microscopes are used for precision measurement.  There are two basic types.
One has a [[reticle]] graduated to allow measuring distances in the focal plane.<ref>{{cite book|first=Gustaf |last=Ollsson |chapter=Reticles |chapter-url=https://books.google.com/books?id=rcrGlrguj1YC&pg=PA2409 |title=Encyclopedia of Optical Engineering, Vol. 3 |publisher=CRC Press |isbn=978-0-824-74252-2 |year=2003 |page=2409 |editor-first=Ronald G. |editor-last=Driggers}}</ref>  The other (and older) type has simple [[crosshairs]] and a micrometer mechanism for moving the subject relative to the microscope.<ref>{{cite book|title=Journal of the Royal Microscopical Society, Containing Its Transactions and Proceedings and a Summary of Current Researches Relating to Zoology and Botany (Principally Invertebrata and Cryptogamia), Microscopy, &c. |chapter=Microscopy |chapter-url=https://books.google.com/books?id=evMVAAAAYAAJ&pg=PA716 |year=1906 |page=716}} A discussion of Zeiss measuring microscopes.</ref>

Very small, portable microscopes have found some usage in places where a laboratory microscope would be a burden.<ref>{{Cite web|last=Linder|first=Courtney|date=2019-11-22|title=If You've Ever Wanted a Smartphone Microscope, Now's Your Chance|url=https://www.popularmechanics.com/technology/gear/a29873640/smartphone-microscope-diple/|access-date=2020-11-03|website=Popular Mechanics|language=en-US}}</ref>

==Limitations==
[[File:Ernst-Abbe-Denkmal Jena Fürstengraben - 20140802 125709.jpg|thumb|The diffraction limit set in stone on a monument for [[Ernst Abbe]]]]
At very high magnifications with transmitted light, point objects are seen as fuzzy discs surrounded by [[diffraction]] rings. These are called [[Airy disk]]s. The ''resolving power'' of a microscope is taken as the ability to distinguish between two closely spaced Airy disks (or, in other words the ability of the microscope to reveal adjacent structural detail as distinct and separate). It is these impacts of diffraction that limit the ability to resolve fine details. The extent and magnitude of the diffraction patterns are affected by both the [[wavelength]] of [[light]] (λ), the refractive materials used to manufacture the objective lens and the [[numerical aperture]] (NA) of the objective lens. There is therefore a finite limit beyond which it is impossible to resolve separate points in the objective field, known as the [[Diffraction-limited system|diffraction limit]]. {{cn|date=December 2024}}Assuming that optical aberrations in the whole optical set-up are negligible, the resolution ''d'', can be stated as:

:<math>d = \frac { \lambda } { 2 NA }</math>

Usually a wavelength of 550&nbsp;nm is assumed, which corresponds to [[green]] light. With [[Earth's atmosphere|air]] as the external medium, the highest practical ''NA'' is 0.95, and with oil, up to 1.5. In practice the lowest value of ''d'' obtainable with conventional lenses is about 200&nbsp;nm. A new type of lens using multiple scattering of light allowed to improve the resolution to below 100&nbsp;nm.<ref name="fb">{{cite journal|arxiv=1103.3643|year=2011|doi=10.1103/PhysRevLett.106.193905|title=Scattering Lens Resolves Sub-100 nm Structures with Visible Light|journal=Physical Review Letters|volume=106|issue=19|last1=Van Putten|first1=E. G.|last2=Akbulut|first2=D.|last3=Bertolotti|first3=J.|last4=Vos|first4=W. L.|last5=Lagendijk|first5=A.|last6=Mosk|first6=A. P.|bibcode=2011PhRvL.106s3905V|pmid=21668161|page=193905|s2cid=15793849 }}</ref>

===Surpassing the resolution limit===
Multiple techniques are available for reaching resolutions higher than the transmitted light limit described above. Holographic techniques, as described by Courjon and Bulabois in 1979, are also capable of breaking this resolution limit, although resolution was restricted in their experimental analysis.<ref>{{cite journal|title=Real Time Holographic Microscopy Using a Peculiar Holographic Illuminating System and a Rotary Shearing Interferometer|author1 =Courjon, D. |author2 =Bulabois, J. |year=1979|volume=10|issue=3|pages=125 |journal=Journal of Optics|doi=10.1088/0150-536X/10/3/004|bibcode=1979JOpt...10..125C}}</ref>

Using fluorescent samples more techniques are available. Examples include [[Vertico SMI]], [[near field scanning optical microscopy]] which uses [[evanescent waves]], and [[STED microscope|stimulated emission depletion]]. In 2005, a microscope capable of detecting a single molecule was described as a teaching tool.<ref>{{cite web|title = Demonstration of a Low-Cost, Single-Molecule Capable, Multimode Optical Microscope|url = http://chemeducator.org/bibs/0010004/1040269mk.htm|access-date = 25 February 2009|url-status = live|archive-url = https://web.archive.org/web/20090306183820/http://chemeducator.org/bibs/0010004/1040269mk.htm|archive-date = 6 March 2009|df = dmy-all}}</ref>

Despite significant progress in the last decade, techniques for surpassing the diffraction limit remain limited and specialized.{{cn|date=December 2024}}

While most techniques focus on increases in lateral resolution there are also some techniques which aim to allow analysis of extremely thin samples. For example, [[sarfus]] methods place the thin sample on a contrast-enhancing surface and thereby allows to directly visualize films as thin as 0.3 nanometers.{{cn|date=December 2024}}

On 8 October 2014, the [[Nobel Prize in Chemistry]] was awarded to [[Eric Betzig]], [[William Moerner]] and [[Stefan Hell]] for the development of super-resolved [[Fluorescence microscope|fluorescence microscopy]].<ref name="AP-20141008-KR">{{cite news |last1=Ritter |first1=Karl |last2=Rising |first2=Malin |title=2 Americans, 1 German win chemistry Nobel |url=http://apnews.excite.com/article/20141008/nobel-chemistry-e759dff699.html |date=8 October 2014 |work=[[AP News]] |access-date=8 October 2014 |url-status=live |archive-url=https://web.archive.org/web/20141011003419/http://apnews.excite.com/article/20141008/nobel-chemistry-e759dff699.html |archive-date=11 October 2014  }}</ref><ref name="NYT-20141008-KC">{{cite news |last=Chang |first=Kenneth |title=2 Americans and a German Are Awarded Nobel Prize in Chemistry |url=https://www.nytimes.com/2014/10/09/science/nobel-prize-chemistry.html |date=8 October 2014 |work=[[New York Times]] |access-date=8 October 2014 |url-status=live |archive-url=https://web.archive.org/web/20141009095518/http://www.nytimes.com/2014/10/09/science/nobel-prize-chemistry.html |archive-date=9 October 2014  }}</ref>

====Structured illumination SMI====
SMI (spatially modulated illumination microscopy) is a light optical process of the so-called [[point spread function]] (PSF) engineering. These are processes which modify the PSF of a [[microscope]] in a suitable manner to either increase the optical resolution, to maximize the precision of [[distance]] measurements of fluorescent objects that are small relative to the [[wavelength]] of the illuminating light, or to extract other structural parameters in the nanometer range.<ref>{{cite book|doi=10.1117/12.336833|title=Laterally modulated excitation microscopy: improvement of resolution by using a diffraction grating|year=1999|last1=Heintzmann|first1=Rainer|editor-first1=Irving J. |editor-first2=Herbert |editor-first3=Jan |editor-first4=Katarina |editor-first5=Pierre M. |editor-last1=Bigio |editor-last2=Schneckenburger |editor-last3=Slavik |editor-last4=Svanberg |editor-last5=Viallet |volume=3568|pages=185–196|series=Optical Biopsies and Microscopic Techniques III|s2cid=128763403 }}</ref><ref>Cremer, Christoph; Hausmann, Michael; Bradl, Joachim and Schneider, Bernhard "Wave field microscope with detection point spread function", {{US patent|7342717}}, priority date 10 July 1997</ref>

====Localization microscopy SPDMphymod====
[[File:3D Dual Color Super Resolution Microscopy Cremer 2010.png|thumb|600px|alt=3D Dual Color Super Resolution Microscopy Cremer from 2010|3D dual color super resolution microscopy with Her2 and Her3 in breast cells, standard dyes: Alexa 488, Alexa 568 LIMON]]
SPDM (spectral precision distance microscopy), the basic localization microscopy technology is a light optical process of [[fluorescence microscopy]] which allows position, distance and angle measurements on "optically isolated" particles (e.g. molecules) well below the theoretical [[limit of resolution]] for light microscopy. "Optically isolated" means that at a given point in time, only a single particle/molecule within a region of a size determined by conventional optical resolution (typically approx. 200–250&nbsp;nm [[diameter]]) is being registered. This is possible when [[molecules]] within such a region all carry different spectral markers (e.g. different colors or other usable differences in the [[light emission]] of different particles).<ref>{{cite journal |doi=10.1007/s00340-008-3152-x|title=SPDM: light microscopy with single-molecule resolution at the nanoscale|year=2008|journal=Applied Physics B|volume=93|issue=1|pages=1–12|last1=Lemmer|first1=P.|last2=Gunkel|first2=M.|last3=Baddeley|first3=D.|last4=Kaufmann|first4=R.|last5=Urich|first5=A.|last6=Weiland|first6=Y.|last7=Reymann|first7=J.|last8=Müller|first8=P.|last9=Hausmann|first9=M.|last10=Cremer|first10=C.|bibcode=2008ApPhB..93....1L|s2cid=13805053 }}</ref><ref>{{cite book|doi=10.1117/12.260797|chapter=Comparative study of three-dimensional localization accuracy in conventional, confocal laser scanning and axial tomographic fluorescence light microscopy|year=1996|last1=Bradl|first1=Joachim|editor5-first=Pierre M|editor5-last=Viallet|editor4-first=Katarina|editor4-last=Svanberg|editor3-first=Herbert|editor3-last=Schneckenburger|editor2-first=Warren S|editor2-last=Grundfest|editor1-first=Irving J|editor1-last=Bigio|title=Optical Biopsies and Microscopic Techniques|volume=2926|pages=201–206|series=Optical Biopsies and Microscopic Techniques|s2cid=55468495 }}</ref><ref>{{cite journal|author1=Heintzmann, R.|author2=Münch, H.|author3=Cremer, C.|year=1997|title=High-precision measurements in epifluorescent microscopy – simulation and experiment|journal=Cell Vision|volume=4|pages=252–253|url=http://www.kip.uni-heidelberg.de/AG_Cremer/sites/default/files/Bilder/pdf_1997/CellVisionVol4No2Heintzmann.pdf|url-status=live|archive-url=https://web.archive.org/web/20160216030456/http://www.kip.uni-heidelberg.de/AG_Cremer/sites/default/files/Bilder/pdf_1997/CellVisionVol4No2Heintzmann.pdf|archive-date=16 February 2016}}</ref><ref>Cremer, Christoph; Hausmann, Michael; Bradl, Joachim and Rinke, Bernd "Method and devices for measuring distances between object structures", {{US patent|6424421}} priority date 23 December 1996</ref>

Many standard fluorescent dyes like [[Green fluorescent protein|GFP]], Alexa dyes, Atto dyes, Cy2/Cy3 and fluorescein molecules can be used for localization microscopy, provided certain photo-physical conditions are present. Using this so-called SPDMphymod (physically modifiable fluorophores) technology a single laser wavelength of suitable intensity is sufficient for nanoimaging.<ref>{{cite journal|author=Manuel Gunkel|pmid=19548231|year=2009|title=Dual color localization microscopy of cellular nanostructures|volume=4|issue=6|pages=927–38|doi=10.1002/biot.200900005|journal=Biotechnology Journal|s2cid=18162278 |display-authors=etal|url=https://hal.archives-ouvertes.fr/hal-00494027/file/PEER_stage2_10.1002%252Fbiot.200900005.pdf |archive-url=https://web.archive.org/web/20190503232308/https://hal.archives-ouvertes.fr/hal-00494027/file/PEER_stage2_10.1002%252Fbiot.200900005.pdf |archive-date=2019-05-03 |url-status=live}}</ref>

====3D super resolution microscopy====
3D super resolution microscopy with standard fluorescent dyes can be achieved by combination of localization microscopy for standard fluorescent dyes SPDMphymod and structured illumination SMI.<ref>{{cite journal|doi=10.1111/j.1365-2818.2010.03436.x|title=Analysis of Her2/neu membrane protein clusters in different types of breast cancer cells using localization microscopy|year=2011|journal=Journal of Microscopy|volume=242|pages=46–54|pmid=21118230|issue=1|display-authors=etal|last1=Kaufmann|first1=R|last2=Müller|first2=P|last3=Hildenbrand|first3=G|last4=Hausmann|first4=M|last5=Cremer|first5=C|citeseerx=10.1.1.665.3604|s2cid=2119158 }}</ref>

====STED====
[[File:MAX 052913 STED Phallloidin.png|thumb|right|300px|Stimulated emission depletion (STED) microscopy image of actin filaments within a cell]]
[[STED microscope|Stimulated emission depletion]] is a simple example of how higher resolution surpassing the diffraction limit is possible, but it has major limitations. STED is a fluorescence microscopy technique which uses a combination of light pulses to induce fluorescence in a small sub-population of fluorescent molecules in a sample. Each molecule produces a diffraction-limited spot of light in the image, and the centre of each of these spots corresponds to the location of the molecule. As the number of fluorescing molecules is low the spots of light are unlikely to overlap and therefore can be placed accurately. This process is then repeated many times to generate the image. [[Stefan Hell]] of the Max Planck Institute for Biophysical Chemistry was awarded the 10th German Future Prize in 2006 and Nobel Prize for Chemistry in 2014 for his development of the STED microscope and associated methodologies.<ref>{{cite web|url = http://www.heise.de/english/newsticker/news/81528|title = German Future Prize for crossing Abbe's Limit|access-date = 24 February 2009|url-status = live|archive-url = https://web.archive.org/web/20090307040808/http://www.heise.de/english/newsticker/news/81528|archive-date = 7 March 2009|df = dmy-all}}</ref>

==Alternatives==
In order to overcome the limitations set by the diffraction limit of visible light other microscopes have been designed which use other waves.{{cn|date=December 2024}}
* [[Atomic force microscope]] (AFM)
* [[Scanning electron microscope]] (SEM)
* [[Scanning ion-conductance microscopy]] (SICM)
* [[Scanning tunneling microscope]] (STM)
* [[Transmission electron microscopy]] (TEM)
* Ultraviolet microscope
* [[X-ray microscope]]

It is important to note that higher frequency waves have limited interaction with matter, for example soft tissues are relatively transparent to X-rays resulting in distinct sources of contrast and different target applications.{{cn|date=December 2024}}

The use of electrons and X-rays in place of light allows much higher resolution – the wavelength of the radiation is shorter so the diffraction limit is lower. To make the
short-wavelength probe non-destructive, the atomic beam imaging system ([[atomic nanoscope]]) has been proposed and widely discussed in the literature, but it is not yet competitive with conventional imaging systems.{{cn|date=December 2024}}

STM and AFM are scanning probe techniques using a small probe which is scanned over the sample surface. Resolution in these cases is limited by the size of the probe; micromachining techniques can produce probes with tip radii of 5–10&nbsp;nm.{{cn|date=December 2024}}

Additionally, methods such as electron or X-ray microscopy use a vacuum or partial vacuum, which limits their use for live and biological samples (with the exception of an [[environmental scanning electron microscope]]). The specimen chambers needed for all such instruments also limits sample size, and sample manipulation is more difficult. Color cannot be seen in images made by these methods, so some information is lost. They are however, essential when investigating molecular or atomic effects, such as [[age hardening]] in [[aluminium alloy]]s, or the [[microstructure]] of [[polymers]].{{cn|date=December 2024}}

==See also==
{{div col|colwidth=30em}}
* [[Digital microscope]]
* [[Köhler illumination]]
* [[Microscope slide]]
{{div col end}}

==References==
{{reflist|30em}}

==Cited sources==
* {{cite book|ref=Van Helden|author1=Van Helden, Albert|author2=Dupre, Sven|author3=Van Gent, Rob |title=The Origins of the Telescope |year= 2011|isbn=978-9069846156|publisher=Amsterdam University Press}}

==Further reading==
* "Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing", Kay Geels in collaboration with Struers A/S, ASTM International 2006.
* [https://arxiv.org/abs/1412.3255 "Light Microscopy: An ongoing contemporary revolution"], Siegfried Weisenburger and Vahid Sandoghdar, arXiv:1412.3255 2014.

==External links==
* [https://www.microscope-antiques.com Antique Microscopes & Scientific Instruments]  A site about Antique Microscopes, their Accessories, and History
* [http://www.antique-microscopes.com Antique Microscopes.com] A collection of early microscopes
* [https://web.archive.org/web/20070419000046/http://www.musoptin.com/mikro1.html Historical microscopes], an illustrated collection with more than 3000 photos of scientific microscopes by European makers {{in lang|de}}
* [http://golubcollection.berkeley.edu The Golub Collection], A collection of 17th through 19th century microscopes, including extensive descriptions
* [http://micro.magnet.fsu.edu/primer/anatomy/anatomy.html ''Molecular Expressions''], concepts in optical microscopy
* [https://www.doitpoms.ac.uk/tlplib/optical-microscopy/index.php Online tutorial of practical optical microscopy] at University of Cambridge
* [http://openwetware.org/wiki/Microscopy OpenWetWare]
* [http://ccdb.ucsd.edu/sand/main?stype=lite&keyword=light%20microscopy&Submit=Go&event=display&start=1 Cell Centered Database]

{{Optical microscopy}}

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