G6 Flash question

I'm missing something here, could someone please explain. I know I'm confused.

I hit the function menu, and go down to the flash compensation selection, the menu is set to auto. So it comes up with the flash exposure from -2 thru +2. Not the manual setting for Flash Output.
What I thought I was doing using the -2 thru +2 was adjusting the flash output, but apparently I'm not. I shoot in AV primarily and when the flash in the menu is set to auto the camera is suppose to adjust the flash output of my 420ex automatically correct? When I adjust this down or up what exactly am I doing? I usually adjust it to -1 shooting indoors close range and +1 like at basketball game. I thought I was cranking up or throttling back the flash?

I hope this makes sense.

Or does this confirm what I was doing?

clicky

I guess the next question is what the difference this is vs EV?

Ok after asking my question I did some research, actually I should have done the research first.

Anyways, it seems that if I set the Flash Adjust to either Auto or Manual, it still allows me to adjust the flash output.

Now correct me if I'm wrong,

Auto - allows me to further adjust what the camera has already adjusted based on its metering. This is measured in 1/3 stop increments

Manual - camera adjusts nothing, I controll the flash output totally. This is measured not in "stops" but steps up to Full Power.

Please someone let me know if I am understanding this correctly at this point. Also, why is it for me the camera adjustment in the Auto mode is something I seem to always have to "adjust", because from what I read about E-TLL it should really take care of everything.

TIA

Joe

You have two compensation settings to adjust -- exposure comp. and flash comp. Exposure comp. actually changes the exposure from that which the camera meters. Let's say you are in shutter priority mode with the shutter at 1/100 and the camera decides that the proper exposure would be 1/100 at f/5.6 but you have +1/3 exposure comp. selected. In that case it would actually use 1/100 at f/5.0 -- 1/3 stop faster than what it metered. Of course in manual mode exposure comp does nothing because you set both parameters yourself.

Flash comp. does nothing with the exposure but it adjusts the output of the flash by the amount you select. If you have flash comp set to +1/3 in the situation above, the camera will still use 1/100 at 5.6 because that's what it metered but it will allow the flash to provide 1/3 stop more light than the camera has deemed necessary.

I hope that helps...