focal length


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

  2. the distance between an object lens and its corresponding focal plane in a telescope.

Origin of focal length

1
First recorded in 1745–55
  • Also called focal distance.

Words Nearby focal length

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

How to use focal length in a sentence

  • It contains a telescope made by Fitz, whose focal length is seventeen feet, and its object-glass is twelve and a half inches.

  • The distance from the principal focus to the center of the lens is the focal length or principal focal distance of the lens.

    Physics | Willis Eugene Tower
  • The focal length of double convex lenses of crown glass is about the same as the radius of curvature of either surface.

    Physics | Willis Eugene Tower
  • I used only the back combination of the lens, which gave a focal length of about twenty-two inches.

British Dictionary definitions for focal length

focal length

noun
  1. the distance from the focal point of a lens or mirror to the reflecting surface of the mirror or the centre point of the lens

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for focal length

focal length

[ kəl ]


  1. The distance between the optical center of a lens or mirror to its focal point.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for focal length

focal length

The distance between the focal point of a lens (that is, the point at which the lens will focus parallel rays of light) and the lens itself.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.