Quote Originally Posted by Franglais
he must have been at something like 1/200s f5.6
To add to this, it could be f8 or f11 too which would give a little more depth of field to be sure everyone in the group is in sharp focus. Like the others have said, it's a matter of exposing for the sky (ambient daylight) and adding flash so that the people (the subjects) are not underexposed. This is really nothing other than a fill flash technique, although in this case it's taken to a high level. It's possible that the lights he was using were powerful enough that they could properly expose the people in the shot who were (probably in the shade) at 1/200 and f5.6 (or slightly slower and smaller aperture as I mentioned in the first sentence). It's hard to do stuff like this with small on-camera flash when there's a lot of light and you want to use a small aperture, just not much power. You're limited by equipment - a bit of experimenting outside on a sunny day with flash and you'll quickly see what I mean.

One question though, were you looking at finished images and/or prints with the blue sky? Could it have just been photoshopped in afterwards (probably not uncommon for something like this)? No amount of equipment will clear out an overcast sky!

OTOH, set the camera for Tungsten white balance. Put an amber gels on the flashes. Everything lit by flash (the people) will have proper color balance. The sky and everything else in the background will be blue. This is a good "when all else fails" technique that can sometimes give really nice results in really boring situations.