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Microscope

2007 Schools Wikipedia Selection. Related subjects: Engineering

   Robert Hooke's microscope (1665) - an engineered device used to study
   living systems.
   Robert Hooke's microscope (1665) - an engineered device used to study
   living systems.

   A microscope ( Greek: μικρόν (micron) = small + σκοπεῖν (skopein) = to
   look at) 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. The term
   microscopic means minute or very small, not visible with the eye unless
   aided by a microscope. The microscopes used in schools and homes trace
   their history back almost 400 years.

   The first useful microscope was developed in the Netherlands in the
   early 1600s. There is almost as much confusion about the inventor as
   about the dates. Three different eyeglass makers have been given credit
   for the invention: Hans Lippershey (who also developed the first real
   telescope); Hans Janssen; and his son, Zacharias.

   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.

Types

   A 1915 Bausch and Lomb Optical microscope.
   A 1915 Bausch and Lomb Optical microscope.

   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. The types are the Compound Light, Stereo, and the electron
   microscope.

Optical microscopes

   A stereo microscope is often used for lower-power magnification on
   large subjects.
   A stereo microscope is often used for lower-power magnification on
   large subjects.

   Optical microscopes, through their use of visible wavelengths of light,
   are the simplest and hence most widely used type of microscope. Recent
   research has shown (see Brian J. Ford's research on simple microscopes)
   that even simple microscopes, those with a single small lens, gave
   amazingly clear images to the earliest microscopists. Today compound
   microscopes, i.e., especially those with a series of lenses, 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 1500x
   with a theoretical resolution of around 0.2 micrometres. Specialised
   techniques (e.g., 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.

Electron microscopes

          Electron microscope

          Electron microscope

   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:
     * 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.
     * Transmission electron microscope: passes electrons completely
       through the sample, analogous to 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 sample
   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:
     * Atomic force microscope
     * Scanning tunneling microscope
     * Electric force microscope
     * Magnetic force microscope (MFM)
     * Near-field scanning optical microscope

Point-projection microscopes

   The field emission microscope, field ion microscope, and the Atom Probe
   are examples of point-projection microscopes where ions are excited
   from a needle-shaped specimen and hit a detector. The Atom-Probe
   Tomograph (APT) is the most modern incarnation and allows a
   three-dimensional atom-by-atom (with chemical elements identified)
   reconstruction with sub-nanometer resolution.

Other microscopes

   Acoustic microscopes 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.

   Retrieved from " http://en.wikipedia.org/wiki/Microscope"
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   with only minor checks and changes (see www.wikipedia.org for details
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