I'm assuming that when using this camera with an external unit either
on the hotshoe or via the PC sync port will flash sync at all shutter
speeds - i.e. up to 1/4000 of a sec.
Can anyone confirm this is the case ?
I am getting an S100FS next week likely. Do you have any specific studio strobes in mind? I have access to Profoto, Dynalight, Speedotron, Hensel, Broncolor, Visatec, Norman and probably a few more.
Several aspects of using studio strobes at high shutter speeds need to be kept in mind...
Firstly, some strobes are actually quite slow with regards to their flash duration. For example, a Profoto Pro 7B (portable battery strobe pack) varies from 1/3000 at minimum power to 1/1300 second at full output. On the other hand a Profoto Pro 7A (AC powered) varies from 1/12000 to 1/3000. With a Pro7A at a reduced power setting, there is a good chance you'll be able to get away with a 1/4000 shutter speed since the flash duration will be much shorter than 1/4000... assuming also that the trigger from the camera is perfectly timed with the shutter - see below. On the other hand, I would suggest that a Pro 7B at full power would need to be shot at no more than 1/1000 on the S00FS to ensure the entire pulse is recorded by the camera.
Another issue is that, if I remember reading this correctly, the S100FS has mechanical shutter speeds up to 1/1000 and beyond that, it is "CCD" timed. At which point during the exposure the camera actually triggers the strobes is the other question? For example, is it is somewhat near the end of the exposure cycle, when a (relatively) long duration flash might get cut off in mid-flash, or does the S100FS trigger perfectly, always right at the start of the exposure? When you are dealing with such small fractions of a second, timing is pretty critical!
After all that is said and done, basically I would suggest that simple testing needs to be performed with the actual strobes and power settings you want to use. Just take a series of photos on manual (fixed f-stop) and run through the faster shutter speeds, up to the maximum 1/4000, and see at which point the images start getting dark or shot to shot exposures start getting inconsistent...
One more note is that often the leading and trailing parts of a flash pulse will have different color-temperatures than the average of the whole "pop", so when you increase the output power, thereby increasing the flash duration, you need to be sure the camera isn't tripping the strobes too late and cutting off the trailing end. Of course some cheap strobes are just inconsistent anyway, with regards to color-temperature when you vary the output power, so you may see color inconsistencies even on long (1/125 second, for example) exposures.
Off topic slightly, a trick one can use to freeze action is take multiple packs, attach one head per pack, and dial the power output down to decrease the flash duration. If you want short duration light from a single head, you can get bi-tube heads that connects to two packs at the same time. Half the output from each pack added up in one head, with correspondingly shorter flash duration. Some high-end packs from Broncolor (and others) even allow you to manually dial-in the desired flash-duration on the the control panel of the pack, with a restriction in output power settings when that is done of course - cannot dial in the shortest duration and still get full power!
Anyway, that is probably a lot more than you wanted to hear...
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Regards,
Mike Mander
http://www.sublimephoto.com 
