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Microscope, instrument for producing enlarged images of small objects. In the compound microscope a magnified, inverted image of an object resting on the “stage” (a platform) is produced by the objective lens, or lens system. This image is viewed through the eyepiece (or ocular) lens, which acts as a simple microscope, giving a greatly magnified image. Generally the object is viewed by transmitted light, illumination being controlled by mirror, diaphragm, and “substage condenser” lenses. Near-transparent objects are often stained to make them visible; phase-contrast microscopy, in which a “phase plate” produces a diffraction effect, is an alternative to staining. Objects too small to be seen directly can be made visible in dark-field illumination, in which an opaque disk prevents direct illumination; the object is viewed in the light diffracted from the remaining oblique illumination. Although theoretically the magnifying power of the optical microscope is unlimited, magnifications greater than about 2,000 offer no improvement in resolving power for light of visible wavelengths. The shorter wavelength of ultraviolet light allows better resolution and hence higher useful magnification. For yet finer resolution, physicists use electron beams and electromagnetic focusing. The field-ion microscope, which offers the greatest magnifications is quite dissimilar from the optical microscope. The compound microscope was invented in the early 17th century.

See also: Leeuwenhoek, Anton van.

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