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focometer

[foh-kom-i-ter]
noun Optics.
  1. an instrument for measuring the focal length of a lens or other optical system.

Origin of focometer

First recorded in 1850–55; foc(us) + -o- + -meter
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for focometer

focometer

noun
  1. an instrument for measuring the focal length of a 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