focal length

Fetched 2026-10-26 (cache).

Synonyms: focal lengths

Antonyms: focal lengths

Related words from Datamuse; suggestions, not definitions.

Noun

1. {{lb|en|optics}} A measure of how strongly an [[optical]] system [[converge]]s or [[diverge]]s light, the inverse of [[optical power]]. In the simple case of a single [[convex]] [[lens]], it is the distance along the optical [[axis]] from the principal plane of the lens to the lens's [[focal point]] (where, for instance, the film would be placed in a camera). For more complex or multi-element optical systems, focal length need not correspond to any obvious measurable physical distance.

Source: Wiktionary · CC BY-SA 4.0 (Wiktionary dump) · cached copy, not a rewrite.