Is an imaginary line passing horizontally through the center of a compound lens system.
A line passing through the centers of curvature of a lens or series of lenses in an optical system.
As applied to birefringent crystals in polarized light and DIC microscopy, the path followed by the ordinary wavefront in a birefringent material. Aligned optical systems possess an optical axis consisting of a straight line joining the centers of curvature of lens surfaces contained within the system.
Of a refractive or reflective optical element, the straight line that is coincident with the axis of symmetry of the surfaces.
Of an antenna, a line parallel to, but offset from, the electrical axis of an antenna. This axis is offset by the distance necessary to have the optical sighting device removed from the electrical center of the antenna.
Optical centerline that passes through the center of a lens or mirror, etc.
The optical center-line of a lens or system. The line passing through the centers of curvature of the optical surfaces of a lens.
The line passing through both centres of curvatures of the optical surfaces of a lens; the optical centreline for all the centres of a lens system.
In an 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 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.