I've had the 5D Mk2 for a few days now, and I'm very impressed - especially since I added the EF 24-70 f2.8.

One thing is puzzling me though - with the camera set to an auto mode (Av, Tv or P) I can't get the exposure compensation to work using either the Main Dial or the Quick Control Dial as per the instruction manual.

With the Power / Quick Control Dial Switch set to activate the Quick Control Dial, I half press the shutter button, then move the main Q/C dial but it doesn't shift the exposure at all.
Same goes for the Main Dial - no effect.

I can adjust it in the Menu - and if I press the Multi Controller, I can adjust it on the LCD Monitor.

I won't ask if anyone can shed any light on this, but help would be appreciated. I'm sure I've simply overlooked something.

Depress the shutter halfway, let it go, and then adjust exposure compensation with the big dial on the back of the camera.

About 5 seconds after you let go of the shutter button, the camera will "sleep" (don't know if this is the right term, but the numbers in the viewfinder go off), and you can't adjust Ev anymore.

That's what I'm doing, but nothing happens. I know you have to do it within a few seconds of half pressing the shutter.

Works fine when I do it in the Menu and if I press the multi controller button.

It must be a setting I've inadvertently used - maybe I'll reset the camera if nobody can think why it won't work.

Weird. See if you can apply a firmware update.

If you hold the button halfway down and twirl while you're doing it, does that work? I'm trying to picture in my mind how I do it.

Thanks again for your help, Mike,

My firmware is 2.0.9 - as far as I can gather from the Canon (UK) site, this is the latest version.
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Makes no difference if I hold down the shutter release button - with the Power Switch set to activate the Quick Control Dial, twirling the dial with the shutter release held down, scrolls between the nine focus points.

With the Power Switch set to 'On', nothing happens at all when I twirl the QCD.

If I twirl the Main Dial (on the top of the camera) with the shutter button held down, it changes the aperture / shutter speeds.

Well, I fixed it . . .
Not sure how, but I fiddled with the menus and now all's working well again.

I wonder whether there's anyone on the planet who actually knows ALL the functions of ALL the menus on this remarkable instrument.
(I certainly don't)!