Welcome to the Digital Photography Academy! This site offers some tips and techniques to improve one's photography skills and some creative ways to manipulate pictures and shooting styles. For a start, feel free to look at the terminology guide.
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Sunday, June 7, 2009

Guide number

Guide number is commonly used as a standard to measure how far a flash can illuminate an object at a specific ISO and aperture. A high guide number indicates a powerful flash while a low guide number refers to a weak flash. Guide number is given in a formula as shown below:

Guide Number = distance x f-stop (at a specific ISO)

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