definitions

focal length

noun Optics.

the distance from a focal point of a lens or mirror to the corresponding principal plane. Symbol: f
the distance between an object lens and its corresponding focal plane in a telescope.

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Nearby words

focal depth, focal distance, focal epilepsy, focal glomerulonephritis, focal infection, focal length, focal necrosis, focal plane, focal point, focal ratio, focal reaction

Origin of focal length

First recorded in 1745–55
Also called focal distance.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for focal distance

focal length

focal distance

noun

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

Medicine definitions for focal distance (1 of 2)

focal distance

n.

focal length

Medicine definitions for focal distance (2 of 2)

focal length

n.

The distance from the surface of a lens or mirror to its focal point.focal distance focus
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for focal distance

focal length

[ fō′kəl ]

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.

Culture definitions for focal distance

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.