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.

Optical resolution

A lens magnifies by bending light (see refraction). Optical microscopes are restricted in their ability to resolve features by a phenomenon called diffraction which, based on the numerical aperture (NA or A_N) of the optical system and the wavelengths of light used (lambda), sets a definite limit (d) to the optical resolution. Assuming that optical aberrations are negligible, the resolution (d) is given by:

Related Topics:
Light - Refraction - Diffraction - Numerical aperture - Wavelength - Optical resolution - Optical aberration

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:d = rac { lambda } { A_N }

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Usually, a lambda of 550 nm is assumed, corresponding to green light. With air as medium, the highest practical A_N is 0.95, and with oil, up to 1.5.

Related Topics:
550 nm - Green - Air

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Due to diffraction, even the best optical microscope is limited to a resolution of 0.2 micrometres.

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