It might have to do with the pulse length of the flash, which I intend to measure with a scope and a photodiode. If the flash pulse is 1/500 s long, then when you open the shutter for 1/1000 of a second, you get half the light since the flash is still spewing out light when the shutter closes again. So what you said makes sense. The reach is dependent on the amount of light and the duration. So twice the distance and cutting the light in half would require 4 times the light. The feedback on the camera measures and compensates but can't make up for the timing part.Originally Posted by Photo-John