High shutter speed sync is the mode that many photographers using Speedlites rave about but in practice its applications even with the latest greatest Canon bodies is limited.
It’s a very pricey feature because you have to buy the top-of-the-line Speedlite.
Every camera body has a maximum flash sync speed for normal operation usually 1/200 sec but sometimes you can get away with using 1/320 sec.
With the fancier Speedlites which cost a lot more, you can flip on a feature on the Speedlite which allows you to shoot your flash at higher shutter speeds so you can use your flash at higher shutter speeds presumably so you can shoot at wider apertures.
In bright sunlight, the typical exposure is in the neighborhood of ISO 100 1/250@ f11.
Even with a telephoto lens, f11 is way too much depth-of-field especially for a portrait situation.
Those instances when we need it most, when it’s super bright outside, we have to be realistic that a dinky 4-AA-battery-powered-flash will never be able to overpower the sun.
You might stand a chance if you double up or even and use 3 Speedlites together and you’re only lighting one subject and their placement is almost on top of your subject.
If nothing else, combining more than one will allow your Speedlites to recycle faster.
I got an email from Brad (who didn’t leave a last name or any other details) asking if E-TTL and High Shutter Speed Sync works with older camera bodies.
I can confirm both modes work on the new Canon Speedlite 600EX-RT with my two bodies: the Canon 5DMark2 and Canon 40D.
When shooting in bright sunlight, the best workaround to control the depth-of-field when using flash in those situations is still slapping on a neutral density filter which you can fine tune by rotating the filter much like a polarizing filter.
They are pricey and they are called a fader filter.