[reknelb]

High-speed sync is another flash feature that sounds great for action—with it, you can shoot flash photos at higher than normal shutter speeds, especially handy for fill-flash in sunlight. But as is the case with strobe mode, the flash fires at very low power in high-speed sync mode, so the flash unit must be positioned very close to the subject. (And exception is leaf-shutter medium-format cameras, which sync at all shutter speeds even with the flash at full power. But these cameras have fairly slow top shutter speeds—generally, 1/500 or thereabouts.)

Hmmmmmm.... Taken from the shutterbug site from an action shot article

here's the link Shutterbug: Action Photography

[roy]

On another note, what would be the point of buying a hss flash if they are a non factor for action??

i have no idea except for the fill flash in daylight. i wish i had read this thread a year+ ago. it may have saved me some $$.. altho i probably would have gotten the super anyway. i did not delve to the depth i should have when researching HSS flash. i was going to use it for macro but the regular 1/180 sync is as good. live and learn.

[Entropy]

OK, I have to admit, I'm not a big fan of flash photography. I think the shots look terrible. I usually bounce whenever possible, or diffuse. I realize that a flash will help stop action, I just didnt realize how much it would help. I'm was looking for a hss flash to shoot indoor arena horse show events. Usually 1/500 under normal conditions will freeze action, sometimes there will be a little blur in the hooves. So I figured a high speed sync flash do the trick. That was an interesting article but, the 1/250 pic with the flash still shows a little motion. I want crisp shots, and my flash only syncs up to 1/180. ???? So I went and shot some pics of the only running/trotting thing available to me right now, my poodle. Turns out, 1/180 with a flash freezes action pretty good. You learn something everyday. I'll post some of the shots after dinner. Thanks for all the info.

On another note, what would be the point of buying a hss flash if they are a non factor for action??

From what I've seen, the primary use for HSS flash is when (for whatever reason) you want to overpower ambient light with the flash, and need a reduced shutter speed to do so. One possibility might be a severely backlit sunset portrait - fast "real" shutter speed needed to reduce background exposure, but need flash for the subject.

Browse around the Strobist archives, lots of good info on flashes, and HSS comes up in a few of their good articles.