Optical axis

An optical axis is an imaginary line that passes through the geometrical center of an optical system such as a camera lens, microscope or telescopic sight.[1] Lens elements often have rotational symmetry about the axis.The optical axis defines the path along which light propagates through the system, up to first approximation.For a system composed of simple lenses and mirrors, 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 systems.
Optical axis (coincides with red ray) and rays symmetrical to optical axis (pair of blue and pair of green rays) propagating through different lenses.
Optic axis of a crystalopticalcamera lensmicroscopetelescopic sightrotational symmetrylensesmirrorsoff-axis optical systemsoptical fiberfiber coreRay (optics)Cardinal point (optics)Antenna boresightpublic domain materialGeneral Services AdministrationDictionary of Military and Associated TermsUnited States Department of Defensephysics