Hi Doug,
I see there are different considerations of the shutter time or "window".
Ultra short flash duration: The "window" is the time for the slit of the DSLR cloth or metal shutter to traverse the sensor plane. If the flash is ultra short in duration, only part of the light sensitive surface will have been reached!
The solution to this, for example with a Canon flash, is to use it in the high frequency mode, where multiple short pulses will illuminate the slit throughout it's travel. I can't imagine how one does this with an Alien Bee in slave mode! Does anyone know?
Prolonged flash duration problem: Here the total duration of the shutter being open (or the slit moving) is too short for the flash duration! This is an issue with classic strobe units, for example, with Lumedyne basic units, when all of 1,600 W/S are put into 1 flash tube. The flash duration can then be as much 1/100 second or longer. That means a portion of the light will not be used and one will get the strange result that as one increases the flash power, the images get no brighter!
So one is not using all the light. Ideally, the peak of the light should be broad enough so the light let in by the moving slit is evenly passed over the sensor surface.
The solution for this issue is two-fold. First split the power to more than one flash tube. for each split one halves the flash duration. Next decrease the shutter speed. For older flash units a synch speed of 1/100 or 1/60 even may be best when using fill power to one tube.
Then again, what is the advantage of this system over Pocket Wizards which work with any brand of studio strobes? So I'd love to hear from a RadioPopper user to know what drives this interest?
Asher