Glossary

Refraction index: for a transparent medium, ratio between the light speed in the air and the light speed in the medium ; for a reflective surface in the air or vacuum, the refraction index is « - 1 »
Lens: optical component with two refractive surfaces axially symmetrical for redirecting the light in a controlled manner
Center thickness: for an optical component or system centered on an optical axis, distance between the vertexes of the first and the last optical surface
Effective focal length: algebraic distance from the primary/secondary principal plane of an optical system to its front/back focal plane
Vertex: top of a surface
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
Secondary principal plane: plane conjugate by an optical system of an object plane ( the primary principal plane ) with a transverse magnification of +1
Front focal length: for an optical system, algebraic distance from the vertex of the first surface to the front focal point
Back focal length: for an optical system, algebraic distance from the vertex of the last surface to the back focal point
Object space: space considered before transformation of light rays by an optical system
Image space: space conjugate of the object space by an optical system