Optical axis
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[[Image:Optical axis en.png|thumb|300px|Optical axis (coincides with red ray) and rays symmetrical to optical axis (pair of blue and pair of green rays) propagating through different lenses.]]
In [[optics]], the term '''optical axis''' is used to define a direction along which there is some degree of [[rotational symmetry]]. It can be used in several contexts:
* In an [[optics|optical]] system, the optical axis is an imaginary line that defines the path along which light propagates through the system. For a system composed of simple [[lens (optics)|lenses]] and [[mirror]]s, the axis passes through the center of curvature of each surface, and coincides with the axis of [[rotational symmetry]]. The optical axis is often coincident with the system's mechanical axis, but not always, as in the case of [[off-axis optical system]]s.
*In an [[Index_ellipsoid#Uniaxial_indicatrix|uniaxial]] [[birefringence|birefringent]] material, the optical axis is the axis of optical anisotropy.
*For an [[optical fiber]], the optical axis is along the center of the fiber core, and is also known as the ''fiber axis''.
==See also==
*[[Ray (optics)]]
*[[Cardinal point (optics)]]
==References==
*[[Federal Standard 1037C]]
*[[Department of Defense Dictionary of Military and Associated Terms]]
[[Category:Geometrical optics]]
[[Category:Fiber optics]]
[[de:Optische Achse (Film)]]
[[eo:Optika akso]]
[[ko:광축]]
[[nl:Optische as]]
[[ja:光学軸]]
[[pl:Oś optyczna]]
[[ru:Оптическая ось]]
[[sk:Optická os]]
[[uk:Оптична вісь]]
[[zh:光轴]]