Alright, here is one for you photo detectives. This was posted on Hammond's blog, looking at the FxIF on it, its flash at 1/500th on a 1D mk IV, which has a max sync speed of 1/300th. As some of you (RR) are now in the stadiums, I was wondering if you knew if some arenas are now using hi speed sync flashes (multiple flashes for the duration of the shutter), or is it a really, really slow flash that burns for the whole shutter action? Or something else going on?
For those unclear about max sync speeds, with slower shutter speeds what happens is the front curtain of the shutter opens fully, the flash is fired, then the rear curtain falls. With higher shutter speeds (above 1/300th in the case of the 1d mk IV) the front curtains starts to fall, then before it reaches the bottom, the rear curtain starts to fall, so you get a slit traversing the frame. If you try and use a flash when beyond the max sync speed, only the slit between the two curtains will be exposed (either the very top or very bottom of the frame depending if you are using front or rear curtain sync) because flash duration is usually very fast (studio flashes are somewhere in the range of 1/6000s for t.5, 1/2000 for t.1), and will extinguish well before the slit has time to traverse the whole frame.
Thoughts? You used to see this every so often, but it was always with a CCD camera that had an electronic shutter (original 1D). No idea how he is doing it with a mechanical shutter.