Definitions for focal length

This page provides all possible meanings and translations of the word focal length

Random House Webster's College Dictionary

fo′cal length`(n.)

  1. the distance from a focal point of a lens or mirror to the corresponding principal plane.

    Category: Optics

Princeton's WordNet

  1. focal distance, focal length(noun)

    the distance from a lens to its focus


  1. focal length(Noun)

    The distance at which something (e.g. a lens, mirror etc.) is in focus; in air it is the distance along the optical axis from a "principal plane" of the lens to one of the lens's focal points.


  1. Focal length

    The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more strongly, bringing them to a focus in a shorter distance. In most photography and all telescopy, where the subject is essentially infinitely far away, longer focal length leads to higher magnification and a narrower angle of view; conversely, shorter focal length or higher optical power is associated with a wider angle of view. On the other hand, in applications such as microscopy in which magnification is achieved by bringing the object close to the lens, a shorter focal length leads to higher magnification because the subject can be brought closer to the center of projection.


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