Term - Guide number
|Guide number||SWPP Photographic Glossary|
Saturday 30th May 2015
Indicates the output, or power, of an electronic flash. You can use the guide number to work out the aperture or flash to subject distance by dividing either into the guide number. A photo term sometimes used to describe a flash factor, which provides a guide to correct exposure when using flash.
Information provided by: SWPP
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