An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The focal length of an imaging system, which consists of several lenses or mirrors.

→ effective; → focal length.

The distance between the optical center of a lens, or the surface of a mirror, and its focus.

→ focal; → distance.

An approximate value of the → focal length, used for the classification of lenses, mirrors, or cameras, as opposed to the measured one.

→ nominal; → focal; → length.