Hi howard,
I really don't understand too much about the minimum distance. I did a test once
by putting some 3200 ISO film in the camera and shooting at macro distance (At
that moment it was with the 28-135IS w/ extension tubes) even wide open the
flash was able to reduce its output to match the conditions.
You can visually test it by increasing the ISO in you camera (don't use film,
it's just a waste), focusing as close as you can and letting the flash go...
you'll see that the higher the ISO, the lower the output, to a point that's
almost nothing, where the E-TTL preflash is even stronger than the real thing.
To be able to distinguish pre-flash from flash, use FEL to lock the flash output
and then shoot with your favorite method (I normally use the RC-1 for macro
work).
BE AWARE that E-TTL measures the reflected light, so it's influenced by subject
tonality. In macro setups, where likely the subject fills the frame you've to be
aware of that and introduce the right flash compensation. You can also FEL from
a grey card.
Have fun!
Gerard.
PS: if you're looking for a Macro bracket, have a look at Manfrotto 330. I got
mine last week and it's a sturdy piece of equipment. Very solid feeling. Just
great.
I'm sure Julian can also comment on it ;-).
BTW: Julian: I'm planning to drill the hole for the stop pin in the flash
socket. I'll let you know afterwards.
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