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glossary

Lens: optical component with two refractive surfaces axially symmetrical for redirecting the light in a controlled manner
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
Effective focal length: algebraic distance from the primary/secondary principal plane of an optical system to its front/back focal plane