I'm working with a friend on getting set up in off camera flash for his small-newspaper job as sports editor. He uses a Rebel with a 420 EX on camera flash. His publisher has given him limited budget to upgrade to a two flash set up.
I use Quantum radio units and know it's beyond his budget so I suggested getting an ST-E2 with another flash.
Here's my question to those who have used the Canon transmitter. What has been your experience in using the unit indoors, in gyms in particular? What about line-of-sight issues? Any problems if the flash units are slightly behind you as opposed to to the sides or in front?
I've had no problem with line of sight so far. I sometimes use the flash slightly behid the camera setup. But I haven't tried a setup where the flash is obstructed from view completely.
I love my ST-E2 indoors, but i wouldn't expect it to cover much area in a gym.
Best is to get a 580 ex, The newer one (the II) is expensive, a used one or even the older first version is great if you can find one, or even a 550 if you can. The idea is to put the new flash on the hot shoe to serve as a master trigger and fill light for the 420 of camera.
The big master will send a signal in a large indoor area pretty reliably (maybe not all the way across a gym :-).
You should be able to get useful info if you re-post in the sports shooting forum.