Today I took my 580EX and a light meter to see if I could understand how the 580EX actually works. I did this in the shade late in the evening and off camera so I could see how the compensation worked using ETTL comparing the background while using EC on the flash .
My dedicated meter may be damaged, but if not, I came to these conclusions, which I do not know if they are correct:
--ETTL: The FC on the flash from -3 to +3 is only one full stop.
--Manual: The flash works like any low powered strobe, but weaker and less control, from 1/64th to full power.
Also:
If my meter is not damaged, it was giving me some very erroneous results. For instance, it was calling for up to two stop increased exposure, which then blew the image totally. This was when I was using it as a incident meter, not as a reflected meter. When used as a reflected meter, the readings were the same, or nearly the same.
Is it possible that the external meter can't for some reason read the 580's flash correctly when in incident mode?
Can anyone with a dedicated meter test this using the 580EX in either manual or ETTL with FC?