akânun, bikânun (#)
Describing a lens or optical system with a convergent power of zero, whose object and image points stretch to infinity. Thus, → afocal system.
Fr.: système afocal
An optical system with object and image points at infinity.
→ afocal; → system.
effective focal length
derâzâ-ye kânuni-ye oskarmand
Fr.: longueur focale effective
The focal length of an imaging system, which consists of several lenses or mirrors.
Of or relating to a focus; placed at or measured from a focus.
Fr.: distance focale
same as → focal length.
Fr.: longueur focale
The distance between the optical center of a lens, or the surface of a mirror, and its focus.
Fr.: plan focal
A plane at right angles to the principal axis of a lens or mirror on which the best image is formed.
Fr.: point focal
Same as → focus.
Fr.: rapport focal
The ratio of the → focal length of a reflecting surface or lens to its effective diameter, i.e. to its → aperture. The smaller the focal ratio, the smaller the image scale and the more luminous the image for a given aperture.
kâhande-ye kânuni, bâzhâzande-ye ~
Fr.: réducteur focal
nominal focal length
derâzâ-ye kânuni-ye nâmin
Fr.: distance focale nominale
An approximate value of the → focal length, used for the classification of lenses, mirrors, or cameras, as opposed to the measured one.