Microscope
A
microscope (
Greek:
micron = small and
scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided
eye. The
science of investigating small objects using such an instrument is called
microscopy, and the term
microscopic means minute or very small, not easily visible with the unaided eye. In other words, requiring a
microscope to examine.
The most common type of microscope—and the first to be invented—is the
optical microscope. This is an
optical instrument containing one or more
lenses that produce an enlarged image of an object placed in the focal plane of the lens(es). There are, however, many other microscope designs.
Microscopes can largely be separated into two classes,
optical theory microscopes and scanning probe microscopes.
Optical theory microscopes are microscopes which function through the
optical theory of lenses in order to magnify the image generated by the passage of a
wave through the sample. The waves used are either
electromagnetic in
optical microscopes or
electron beams in
electron microscopes.
Optical Microscopes
Optical microsopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope. They serve uses in many fields of science, particularly
biology and
geology.
Optical microscopes use
refractive lenses, typically of
glass and occasionally of
plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 100x with a
resolution of up to 0.2
micrometres. Specialised techniques (eg.
scanning confocal microscopy) may exceed this magnification but the resolution is an insurmountable
diffraction limit.
Other microscopes which use
electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a
vacuum like electron microscopes, is the
x-ray microscope.
Because of their popular use, optical microscopes have many adaptions to facilitate usage and improve image quality.
Electron microscopes
Electron microscopes, which use beams of
electrons instead of light, are designed for very high magnification usage. Electrons, which have a much smaller wavelength than visible light, allow a much higher resolution. The main limitation of the electron beam is that it must pass through a
vacuum as air molecules would otherwise scatter the beam.
Instead of relying on
refraction, lenses for
electron microscopes are specially designed electromagnets which generates magnetic fields that are approximately parallel to the direction that electrons travel. The electrons are typically detected by a
phosphor screen,
photographic film or a
CCD.
Two major variants of electron microscopes exist:
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Scanning electron microscope: looks at the surface of bulk objects by scanning the surface with a fine electron beam and measuring reflection. May also be used for spectroscopy.
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Transmission electron microscope: passes electrons completely through the sample, analogous to basic optical microscopy
basic optical microscopy. This requires careful sample preparation, since electrons are scattered so strongly by most materials. It can also obtain detailed information on the sample's
crystallography through
selected area diffraction.
Scanning probe microscope
In
scanning probe microscopy (SPM), a physical probe is used either in close contact to the sample or nearly touching it. By rastering the probe across the sample, and by measuring the interactions between the sharp tip of the probe and the sample, a
micrograph is generated. The exact nature of the interactions between the probe and the determines exactly what kind of SPM is being used. Because this kind of microscopy relies on the interactions between the tip and the sample, it generally only measures information about the surface of the sample.
Some kinds of SPMs are:
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Atomic force microscope*
Scanning tunneling microscope*
Electric force microscope *
Magnetic force microscopeOther microscopes
Acoustic microscopes use sound waves to measure variations in acoustic impedence. 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.
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Optical Microscope*
Microscopy*
Electron Microscope*
Angular resolution*
Microscope image processing*
Microscope slide*
Microscopy*
Microscopy laboratory in:
A Study Guide to the Science of Botany at Wikibooks
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Telescope*
Common acronyms in microscopy*
Condensed Matter Physics*
X-ray microscope*
Directory of Microscopy & Microanalysis Meetings/ShortCourses/Conferences 2006*
Microscopy images*
A virtual polarization microscope (requires Java)
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WWW Virtual Library: Microscopy *
Micscape - a monthly magazine directed towards the amateur microscopist
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Microscopy*
the optics of the microscope *
Optical microscopy primer*
Royal Microscopical Society*
The Microscope - quarterly journal
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Antique German microscopes history of continental microscopes illustrated with 2000 photos (in German)
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Early American made microscopes Antique American made microscopes and the makers.
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Some Early Microscopes from the Optical Institute in Wetzlar Microscope history.
