Editing Microscope (section)

==Types==
[[Image:MicroscopesOverview.svg|thumb|right|300px|Types of microscopes illustrated by the principles of their beam paths]]
[[File:MicroscopyResolution.png|thumb|300px|Evolution of spatial resolution achieved with optical, transmission (TEM) and aberration-corrected electron microscopes (ACTEM)<ref>{{cite journal|doi=10.1557/mrs2006.4|url=http://web.pdx.edu/~pmoeck/pennycooks%20aberration%20corrected%20microscopes.pdf|title=Materials Advances through Aberration-Corrected Electron Microscopy|journal=MRS Bulletin|volume=31|pages=36–43|year=2011|last1=Pennycook|first1=S.J.|last2=Varela|first2=M.|last3=Hetherington|first3=C.J.D.|last4=Kirkland|first4=A.I.|s2cid=41889433 }}</ref>]]

Microscopes can be separated into several different classes. One grouping is based on what interacts with the sample to generate the image, i.e., [[light]] or [[photons]] (optical microscopes), [[electron]]s (electron microscopes) or a probe (scanning probe microscopes). Alternatively, microscopes can be classified based on whether they analyze the sample via a scanning point (confocal optical microscopes, scanning electron microscopes and scanning probe microscopes) or analyze the sample all at once (wide field optical microscopes and transmission electron microscopes).

Wide field optical microscopes and transmission electron microscopes both use the theory of lenses ([[optics]] for light microscopes and [[electromagnet]] lenses for electron microscopes) in order to magnify the image generated by the passage of a [[wave]] transmitted through the sample, or reflected by the sample. The waves used are [[electromagnetic waves|electromagnetic]] (in [[optical microscope]]s) or [[electron]] beams (in [[electron microscopes]]). [[Optical resolution|Resolution]] in these microscopes is limited by the [[wavelength]] of the radiation used to image the sample, where shorter wavelengths allow for a higher resolution.<ref name=":0">{{Cite journal|last1=Lodish|first1=Harvey|last2=Berk|first2=Arnold|last3=Zipursky|first3=S. Lawrence|last4=Matsudaira|first4=Paul|last5=Baltimore|first5=David|last6=Darnell|first6=James|date=2000|title=Microscopy and Cell Architecture|url=https://www.ncbi.nlm.nih.gov/books/NBK21629/|journal=Molecular Cell Biology. 4th Edition|language=en}}</ref>

Scanning optical and electron microscopes, like the confocal microscope and scanning electron microscope, use lenses to focus a spot of light or electrons onto the sample then analyze the signals generated by the beam interacting with the sample. The point is then scanned over the sample to analyze a rectangular region. Magnification of the image is achieved by displaying the data from scanning a physically small sample area on a relatively large screen. These microscopes have the same resolution limit as wide field optical, probe, and electron microscopes.

Scanning probe microscopes also analyze a single point in the sample and then scan the probe over a rectangular sample region to build up an image. As these microscopes do not use electromagnetic or electron radiation for imaging they are not subject to the same resolution limit as the optical and electron microscopes described above.

===Optical microscope===
{{main|Optical microscope|Digital microscope|USB microscope}}
The most common type of microscope (and the first invented) is the [[optical microscope]]. This is an [[optics|optical]] [[measuring instrument|instrument]] containing one or more [[Lens (optics)|lenses]] producing an enlarged image of a sample placed in the focal plane. Optical microscopes have [[refraction|refractive]] glass (occasionally plastic or [[quartz]]), to focus light on the eye or on to another light detector. Mirror-based optical microscopes operate in the same manner. Typical magnification of a light microscope, assuming visible range light, is up to 1,250× with a theoretical [[Diffraction-limited system|resolution limit]] of around 0.250&nbsp;[[micrometre]]s or 250&nbsp;[[nanometre]]s.<ref name=":0"/> This limits practical magnification to ~1,500×. Specialized techniques (e.g., [[Confocal laser scanning microscopy|scanning confocal microscopy]], [[Vertico SMI]]) may exceed this magnification but the resolution is [[diffraction]] limited. The use of shorter wavelengths of light, such as ultraviolet, is one way to improve the spatial resolution of the optical microscope, as are devices such as the [[near-field scanning optical microscope]].

[[Sarfus]] is a recent optical technique that increases the sensitivity of a standard optical microscope to a point where it is possible to directly visualize nanometric films (down to 0.3&nbsp;nanometre) and isolated nano-objects (down to 2&nbsp;nm-diameter). The technique is based on the use of non-reflecting substrates for cross-polarized reflected light microscopy.

[[Ultraviolet]] light enables the resolution of microscopic features as well as the imaging of samples that are transparent to the eye. [[Near infrared]] light can be used to visualize circuitry embedded in bonded silicon devices, since silicon is transparent in this region of wavelengths.

In [[fluorescence microscopy]] many wavelengths of light ranging from the ultraviolet to the visible can be used to cause samples to [[fluorescence|fluoresce]], which allows viewing by eye or with specifically sensitive cameras.[[File:Brightfield phase contrast cell image.jpg|thumb|Unstained cells viewed by typical brightfield (left) compared to phase-contrast microscopy (right)]]

[[Phase-contrast microscopy]] is an [[optical microscope|optical microscopic]] illumination technique in which small [[phase shifts]] in the light passing through a transparent specimen are converted into [[amplitude]] or [[contrast (vision)|contrast]] changes in the image.<ref name=":0"/> The use of phase contrast does not require [[staining]] to view the slide. This microscope technique made it possible to study the [[cell cycle]] in live cells.

The traditional optical microscope has more recently evolved into the [[digital microscope]]. In addition to, or instead of, directly viewing the object through the [[eyepiece]]s, a type of sensor similar to those used in a [[digital camera]] is used to obtain an image, which is then displayed on a computer monitor. These sensors may use [[CMOS]] or [[charge-coupled device]] (CCD) technology, depending on the application.

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 of which is 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 |doi-access=free }}</ref>
[[File:Electron Microscope.jpg|thumb|upright|Modern transmission electron microscope]]

===Electron microscope===

[[File:Cytokinesis-electron-micrograph.jpg|thumb|Transmission electron micrograph of a dividing cell undergoing cytokinesis]]{{main|Electron microscope}}
The two major types of electron microscopes are [[transmission electron microscope]]s (TEMs) and [[scanning electron microscope]]s (SEMs).<ref name=":0" /><ref name=":1">{{Cite journal|last1=Alberts|first1=Bruce|last2=Johnson|first2=Alexander|last3=Lewis|first3=Julian|last4=Raff|first4=Martin|last5=Roberts|first5=Keith|last6=Walter|first6=Peter|date=2002|title=Looking at the Structure of Cells in the Microscope|url=https://www.ncbi.nlm.nih.gov/books/NBK26880/|journal=Molecular Biology of the Cell. 4th Edition|language=en}}</ref> They both have series of electromagnetic and electrostatic lenses to focus a high energy beam of electrons on a sample. In a TEM the electrons pass through the sample, analogous to [[bright field microscopy|basic optical microscopy]].<ref name=":0"/> This requires careful sample preparation, since electrons are scattered strongly by most materials.<ref name=":1"/> The samples must also be very thin (below 100&nbsp;nm) in order for the electrons to pass through it.<ref name=":0"/><ref name=":1"/> Cross-sections of cells stained with osmium and heavy metals reveal clear organelle membranes and proteins such as ribosomes.<ref name=":1"/> With a 0.1&nbsp;nm level of resolution, detailed views of viruses (20 – 300&nbsp;nm) and a strand of DNA (2&nbsp;nm in width) can be obtained.<ref name=":1"/> In contrast, the SEM has raster coils to scan the surface of bulk objects with a fine electron beam. Therefore, the specimen do not necessarily need to be sectioned, but coating with a nanometric metal or carbon layer may be needed for nonconductive samples.<ref name=":0"/> SEM allows fast surface imaging of samples, possibly in thin water vapor to prevent drying.<ref name=":0"/><ref name=":1"/>

===Scanning probe===
{{main|Scanning probe microscopy}}

The different types of scanning probe microscopes arise from the many different types of interactions that occur when a small probe is scanned over and interacts with a specimen. These interactions or modes can be recorded or mapped as function of location on the surface to form a characterization map. The three most common types of scanning probe microscopes are [[atomic force microscopy|atomic force microscopes]] (AFM), [[near-field scanning optical microscopy|near-field scanning optical microscopes]] (NSOM or SNOM, scanning near-field optical microscopy), and [[scanning tunneling microscopy|scanning tunneling microscopes]] (STM).<ref name="Bhushan">{{cite book|editor1-last=Bhushan|editor1-first=Bharat|title=Springer handbook of nanotechnology|date=2010|publisher=Springer|location=Berlin|isbn=978-3-642-02525-9|page=620|edition=3rd rev. & extended}}</ref> An atomic force microscope has a fine probe, usually of silicon or silicon nitride, attached to a cantilever; the probe is scanned over the surface of the sample, and the forces that cause an interaction between the probe and the surface of the sample are measured and mapped. A near-field scanning optical microscope is similar to an AFM but its probe consists of a light source in an optical fiber covered with a tip that has usually an aperture for the light to pass through. The microscope can capture either transmitted or reflected light to measure very localized optical properties of the surface, commonly of a biological specimen. Scanning tunneling microscopes have a metal tip with a single apical atom; the tip is attached to a tube through which a current flows.<ref name="Sakurai">{{cite book|editor1-last=Sakurai|editor1-first=T.|editor2-last=Watanabe|editor2-first=Y.|title=Advances in scanning probe microscopy|date=2000|publisher=Springer|location=Berlin|isbn=978-3-642-56949-4}}</ref> The tip is scanned over the surface of a conductive sample until a tunneling current flows; the current is kept constant by computer movement of the tip and an image is formed by the recorded movements of the tip.<ref name="Bhushan"/>
[[File:Leaf epidermis.jpg|thumb|Leaf surface viewed by a scanning electron microscope]]

=== Other types ===
[[Scanning acoustic microscope]]s use sound waves to measure variations in acoustic impedance. Similar to [[Sonar]] in principle, they are used for such jobs as detecting defects in the subsurfaces of materials including those found in integrated circuits. On February 4, 2013, Australian engineers built a "quantum microscope" which provides unparalleled precision.<ref>{{cite web|url=https://www.sciencedaily.com/releases/2013/02/130204163442.htm|title=Quantum Microscope for Living Biology|website=Science Daily|date=4 February 2013|access-date=5 February 2013}}</ref>

====Mobile apps====
[[Mobile app]] microscopes can optionally be used as [[optical microscope]] when the flashlight is activated. However, mobile app microscopes are harder to use due to visual [[Noise (video)|noise]], are often limited to 40x, and the resolution limits of the [[camera lens]] itself.