This is driving me nuts, and I'm not that familiar with using a flash - yet.
I think I understand how ETTL-II on a 580EX II works when the flash is aimed straight ahead but does it work when the flash is used for bounce (with or without the little white card extended)? Or, is this more or less trial and error in getting correct exposure when using bounce?
And, sort or related, am I correct in thinking that the "zoom" function with the flash matching the zoom lens setting only works with the flash head straight ahead, too?
Sorry for the basic question - I'm traveling and only packed the camera manual - didn't bring the flash manual and have never used bounce before.
First, yes it works, as has been discussed.
Second, ETTL doesn't mean you'll be able to stop the lens down and shoot at iso 100, you'll still need to accommodate the limited power of the flash. I normally will try to set the camera to be within at least three stops of ambient light, and then use ETTL to make up the difference on the subject. This may mean using iso 800 and f/2.8, despite using flash. You may find that if the room is quite large you may still need to use iso's as high as 3200; as where you couldn't get the shot before you will be able to with the flash.