Radiance ( radiometry ): for a light source or a diffusing/reflecting surface, power emitted per unit of solid angle and per unit of apparent area
Aperture : diaphragm limiting the number of light rays that are able to propagate
Optical system: in geometrical optics, assembly of optical components for redirecting the light in a controlled manner
Transmission: ratio between transmitted radiation power (or intensity or amplitude) and incident radiation power (or intensity or amplitude)
Secondary principal plane: plane conjugate by an optical system of an object plane ( the primary principal plane ) with a transverse magnification of +1
Irradiance ( radiometry ): optical power received by unit area
Primary principal plane: plane of the object space of an optical system whose conjugation by the said optical system occurs with a magnification of +1 and whose conjugate plane is called the secondary principal plane
