Shel Belinkoff wrote:
What's a "Guide Number" and how does it work?Shel
The Guide number is flash distance times aperture.So a guide number of 30 feet will give a flash working distance of 15' at f2, at f4 it would be 7.5'. Meters work the same way, just in meters.
Minimum distance is 1/5 of maximum distance, so minimum distance in the above example would be 3', generally there's always a minimum coverage distance as well (usually around 2') which is inherent to the flash itself.
-Adam
