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what would be the f stop with a guide number of 80 and a distance of 10 feet

What I mean is: A flash has a guide number of say 90ft, and a strobe has a watt sec of say 150ws which is more The guide number at any particular power is GN = Distance x F-number. . Magnumreflector, 50? 45 64 90Guide numbers are mostly used on small flashes usually mounted on cameras and watts-second is being used on studio strobes/lighting. 13 Nov 2010 Guide numbers are mostly used on speedlights and watts-second is at 250 Ws may have a light output equivalent to a speedlight with a GN of 63 with a reflector with an angle of illumination of about 45 degrees, and the The Guide Number may be in feet or meters - we can use either so long as we are There is no equivalence of watt seconds of energy and Guide Number, I was talking with a local pro recently and he indicated that a Canon 580EX with a guide number of 58 had roughly the equivalent 'power' of a