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DPChallenge Forums >> Hardware and Software >> guide numbers for 580ex
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Canon EOS-5D
05/16/2008 06:40:38 AM · #1
the guide number given for the canon 580 EX11 is 58m at 100 iso does anyone know the guide numbers at other iso settings.
e.g 200, 400, 800, 1600
Canon EOS-5D
Sigma 24-70mm f/2.8 EX Aspherical DF for Canon
 05/16/2008 10:42:33 AM · #2
Just calculate it. Its 58m at ISO 100, f/1.

So at ISO 100 its 58m /

E.g. f/2 is 29m, f/4 is 14.5m, etc.

But at ISO 400, its 192m /

So at f/2 its 96m, f/4 is 58m, etc.

If you want the general equation for the 580, its: distance = 58 meters(ISO used / 100) / (f-stop number)

For the 430ex, substitute 43meters for 58 meters.

BTW, the distance is from the flash, not the camera (which only matters when you use off-camera flash)


Canon EOS-5D
05/16/2008 10:58:45 AM · #3
thanks for that, but still a little confused, the method I have used for years ehen using flash photography is guide number divided by distance in feet to obtain my f stop.

I have the guide number for ISO100 as 58m = approx 190.

you mention guide number for ISO 400 as 192m where has this figure come from.
Canon EOS-40D
Canon EF 24-105mm f/4.0 L IS
 05/16/2008 11:17:35 AM · #4
Try this fun little calculator:
Lighting and DOF calculator
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