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...how well does ettl work if i were to use my 580 through a soft box/ shoot through umbrella/ bouncing off the ceiling?
It works fine; that's how I normally do it with one- or two-light setups -- camera in manual, flash in ETTL.
However, the soft box I use is a Wescott Apollo, and on that one the flash is inside the box, so wireless control with the 7D's popup or even a camera-mounted 580EX is iffy; the sensor on the in-box flash can't reliably see the control pulses from the camera's flash.
What I do in that case is use a long (24-foot) ETTL cord between the camera and the in-box 580EX, using the latter as the Master, and then set my slave 430EX II so the receiver faces the soft box.
This is the ETTL cord I use: http://www.flashzebra.com/products/0125/index.shtml
...if ettl is not going to be useful in such scenarios - then I don't want to spend time over understanding how it works. Would rather have full control and understanding of the flash output each time rather than be guessing on what it's going to spit out based on my metering.
The reason I use ETTL flash most of the time is because my flash-to-subject distance is often dynamic, and it's not always practical to change the settings for manual flash by going over to the box, opening it, reaching in and fiddling with the flash, closing it up, and going back to the camera. It's easier to leave the flash in ETTL mode and adjust it from the camera with FEC. (That is with my 20D. Now that I also have a 7D, which has camera-menu control of manual flash, that has changed, so I may start using manual flash more often.)