Originally Posted by
speedneeder
Kenny, I didn't know the guide numbers were different between the flashes you mentioned.
If they are the same power, then the diffuser, zoom setting, and distance from subject would all make much more difference than the power you select to use. I have a couple 560's, and you select in full power, 1/2, 1/4 etc. Each of these is one stop. Soooo, if you are set at 1/2 power, and you change your aperture from 8.0 to 5.6, I would expect to get the same exposure at 1/4 power on your flash.
I am probably not understanding your question though. I don't use a light meter and talk in f-stops like I have seen some photogs do, I just take the picture and look at my histogram, which you have to do whether you have a light meter or not, and make adjustments as needed.
Is a 'flash meter' something different?