ETTL vs ETTL II
In video clip #3, ETTL II metering the fellow explains that in ETTL II when you press the shutter half way the camera takes an ambient reading, then when the shutter is pressed all the way the flash pre fires. The pre fire determines the difference between the subject and the ambient by the amount of light reflected. Focus and recompose is not supposed to effect the exposure.
He goes on to say that ETTL is focus point linked. So obviously this is how it determines the subject for flash exposure. Pretty basic. I guess the ETTL does not fire a pre flash then? Does flash exposure lock work here as well? I guess I can look that up and I imagine it does but I'm wondering if there are any other bits of helpful information about ETTL there are.
This works for me as when I shoot with two bodies the 580II goes on my 5D2 and my 580 goes on my 7D. I trust my outer focus points more on my 7D.
Another curiosity. My friend just purchased a SB900 and I was over there on the weekend helping him play with it. I think Nikon is focus point linked and it's kind of known Nikon is more accurate. Is is due to the CLS or the focus point linked method. I only ask as it seems he was fine tuning his FEC as often as I was. He probably just has to learn more about it.
The solution is always simple. Getting there is the hard part.