Quote Originally Posted by kintatsu View Post
It's not just the flash duration or battery. With a focal plane curtain shutter, only part of the image is illuminated as the shutter travels across the image plane. With a leaf or diaphragm shutter, the whole image is exposed to the flash, which triggers when the shutter is generally fully open.

If you're using a focal plane shutter, the results of shooting faster than synch are dark bands at one end or side of the image where the flash was not exposed. The faster the shutter, the larger the band. Based on your 1/200 showing underexposed, I would guess a flash synch of 1/30 on a focal plane shutter. The RB-67 uses the leaf shutter, so synch is possible at all speeds the lens can accommodate.
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.

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?