focal length

English

The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.

Noun

focal length (plural focal lengths)

1. (optics) A measure of how strongly an optical system converges or diverges 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.

Derived terms

• calibrated focal length

Translations

distance

• Chinese:

  Mandarin: 焦距 (zh) (jiāojù)

• Czech: ohnisková vzdálenost f
• Danish: brændvidde
• Dutch: brandpuntsafstand (nl) m
• Finnish: polttoväli (fi)
• French: distance focale (fr) f
• German: Brennweite (de) f
• Greek: εστιακή απόσταση f (estiakí apóstasi)
• Hungarian: fókusztávolság (hu), gyújtótávolság (hu)
• Indonesian: jarak pumpun, jarak fokus
• Irish: fad fócasach m
• Japanese: 焦点距離 (ja) (しょうてんきょり, shōten kyori)
• Maori: roa o te ngahunga, roa ngahunga
• Norwegian:

  Bokmål: brennvidde m or f

  Nynorsk: brennvidd f, brennvidde f

• Polish: ogniskowa (pl) f
• Portuguese: distância focal f
• Romanian: distanță focală (ro) f
• Russian: фо́кусное расстоя́ние (ru) n (fókusnoje rasstojánije)
• Swedish: brännvidd (sv) c
• Tagalog: tingubing haba