#3. "RE: Multiple SB910s in Manual?" In response to In response to 2 Thu 04-Apr-13 05:35 PM by gvk
Your calculations are correct. The same ratios can be also applied when diffusers are used as long as the flashes are treated in the same way. For example, I often mount 2 x SB-800s to fire through the same umbrella for my main light either to increase the illumination by a stop, or to reduce recycle time by decreasing the power of both speedlights.