the Ratios for the two independent halves of the macro ring are set A:B.
he third channel C, which is what fires the 580(s) as slave IS ONLY USED TO
ILLUMINATE THE Macro SCENE BACKGROUND, it is not computed as part
of the metered exposure.
So, the 14EX really works like Ratios(A:B):C. Channels A and B do not even
fire the 580 if you set it as slave channel A or B.
If you point the slave on Channel C into the metered scene, the scene will be
overexposed.
This (A:B):C is good for macro work, but it does NOT work the same as the
580EX as a wireless E-TTL master with slaves on A, B, or C channels. The
580 as master does factor multiple slaves on each channel as part of the
exposure.
You CAN vary the ratio between A and B halves of the ring with
ratios. And you vary the C output with FEC. But, these two actions are
independent in terms of exposure
I would recommend M mode for flash (the flash will still be automatic in E-TTL mode).
You might consider going manual, maybe iso 800 or 1600, shutter speed
fast enough to control motion blur and f/stopped down enough to make up
for the lack of light to focus tightly. Maybe 1/80th at 5.6, I'd start
testing there. Let the flash do it's thing. Another thing to test is +
or - flash exp comp, depending on the situation.
In TTL mode the Canon system meters the A:B ratio with a series of
pre-flashes: A then B, then A and B together to adjust the ratio and
exposure of the main foreground subject.
The ability of a flash unit to act as a "slave" to a master flash is
fairly old technology. It's simply a matter of closing a circuit to
fire the flash when the presence of another flash is detected. The term
"slave" has been used for decades to describe this technology.
refer this site for more details on ur 580EX.....
http://super.nova.org/DPR/Canon/
thank you
good luck...