This page is optimized for large screens. Zooming may cause some display problems.

glossary

Aperture : diaphragm limiting the number of light rays that are able to propagate
Effective focal length: algebraic distance from the primary/secondary principal plane of an optical system to its front/back focal plane
F-number: dimensionless number whose inverse value is twice the numerical aperture of an optical system ; for optical systems designed to « work » at infinity, it is commonly assumed as the ratio between the focal length and the aperture diameter