guide number


Also found in: Acronyms, Wikipedia.

guide number

[′gīd ‚nəm·bər]
(graphic arts)
A number that relates the output of a light source (such as a flashbulb) to the sensitivity of a particular film; when the number is divided by the distance in feet to the subject, it gives the T stop at which the lens should be set.
References in periodicals archive ?
I've stood for awestruck moments on the eastern slope of Table Mountain, a flattened pile of windfaceted sandstone so enormous it seemed to thrum; then guide number one whisked me away.
With a guide number of 112 feet at ISO 100 the SB-910's power will blind you silly.
The anticipated cable television reference guide number has not been officially released.