Dictionary.com
Thesaurus.com

T number

American  

noun

Photography.

  1. one of a series of calibrations of lens openings according to the intensity of the light actually transmitted by the lens. T

T-number British  

noun

  1. photog a function of the f-number of a camera lens that takes into account the amount of light actually transmitted by 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

Etymology

Origin of T-number

from T ( otal Light Transmission ) Number

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.