EX series ratio question.

[smudge]

Can someone help with this I have looked through my manual(580+20D) and cannot find a definite answer.

I have two 580 ex and one 550ex. What I would like to do is using ETTL for exposure, set A:B to expose the subject C for B/G, but I want to use one unit for on camera based fill. According to my manual on camera is Master and not assigned a Slave ID. Does this mean, that with the master active(on) there can effectively be four groups, or does the master act as a group, if so how do I set an I.D for it.

[scottbergerphoto]

The on camera flash (master) defaults to Group A. Then set your two other flashes to B and C. You set the ratios (A:B):C. So if A is fill as it usually is, then set your ratio as something like (1:2):1
I used that set of ratios here:
http://www.pbase.com/scottbergerphoto/ayana_bailey
You will also find instructions on how to do it here:
http://photography-on-the.net/forum/showthread.php?t=46778&highlight=

[smudge]

Thanks Scott. Thats kind of what I thought. Good to see the results though in your portrait. It works really well. My wife is now going to be annoyed for the next two hours while I check it out.