Correct. Focal plane shutters usually have a max sync speed of 1/250s. I was testing my theory on a Nikon D700 which has has it's top speed at 1/250s. Also, my testing involved a Mamiya RZ67 with leaf lenses. In another thread here, I've posted some samples of my findings. But I think I might need to make a thread in the lighting section rather than the Medium Format one.
Originally Posted by kintatsu
None the less, I think that flash duration has something to do with underexposure because if it's short and isn't at full power while the shutter is open, then wouldn't the light hitting the film/sensor not be at metered?