My 20D keeps underexposing images in P/Av mode

I just noticed this now, but all shots in P mode (a majority) are being underexposed by 1 1/3 and I can't figure out what option in the menu will fix this. I've read the manual - I must be missing something but I can't figure out what. The only way I can stop this for now is to shoot in M mode, except that sometimes I need to take a shot fast and I don't have time to flip through the right settings to expose it properly.

Are you sure they are underexposing? Try shooting a gray card in manual and automatic modes with the same settings.

SolidxSnake wrote in post #6045655
Are you sure they are underexposing? Try shooting a gray card in manual and automatic modes with the same settings.

On the little meter at the bottom of the top LCD screen it's about one stop to the left. The playback screen says +/- 1 1/3, that's how i know the exact number. No amount of top wheel turning will change it. And I loaded a sky shot just a few minutes ago and it was wayyy too dark.

If it helps...I shoot in AWB, WB shift/bracketing is 0, color temp is 5200K.

I'll try the gray card trick.

EDIT: Okay, so I shot my old gray Nikon camera (not 100% gray) at f/3.5 1/25. Histograms are about the same and it says +/- 1 1/3 next to the image shot in P mode.

You must've been adding some EC then. Slide the power button to the uppest position (the line above the ON), half-press the shutter button then turn the dial on the back until the EC mark goes back in the center while looking in the viewfinder.

adas wrote in post #6045730
You must've been adding some EC then. Slide the power button to the uppest position (the line above the ON), half-press the shutter button then turn the dial on the back.

Thanks, that worked beautifully. EDIT: Although, to be honest, I don't know how that even happened...I normally don't touch the wheel when I half-press the shutter.

I think the problem might be that you have dialled some exposure compensation in at some stage in the past, either knowingly or unknowingly (its scarily easy to do by accident).

On my 30D, no amount of playing with the "top wheel" (AKA the main dial) will alter anything either. You need to turn the quick control dial on the rear of the body to bring the exposure compensation back to zero.

Have a play and let us know. Dont forget the dial needs to be turned on before it will do anything.

Sorry Guys, While I was typing, you had posted!

hbdragon88 wrote in post #6045741
Thanks, that worked beautifully. EDIT: Although, to be honest, I don't know how that even happened...I normally don't touch the wheel when I half-press the shutter.

Yes you do, in M mode. And it's easy to do it in other modes then. Keep the power button to ON for a while, that will inactivate the back-wheel, if you don't need EC.

adas wrote in post #6045802
Yes you do, in M mode. And it's easy to do it in other modes then. Keep the power button to ON for a while, that will inactivate the back-wheel, if you don't need EC.

When I half-press. I was fairly certain that all i did was move the wheels around and then * and click the shutter. And a lot of old shots (I didn't start seriously using M mode until Friday) were also underexposed.

Okay, I just found out that I don't even need to half-press the shutter in P mode to move the EC around. I probably did it then.

The dial can move simply by rubbing against your body while slung round your kneck IF the on/off switch is turned to allow it. I ruined a good half dozen films in my Eos-3 and was subsequently told that many pros taped the dial up to prevent expensive accidents. It really taught me a lesson.

The EC on the back dial is only active within 6 sec. after half-pressing the shutter button.
Never once happened to me to turn it inadvertently other than with my hand. Though sometimes I bump the button in the middle of that dial (which is set to preview on) with my nose.

In M you don't have to start metering to change the setting. I'm not sure if on one of the three automatic modes you'd have to, though it makes sense that you do.

Yes, in any automatic mode it is as was stated above: You can change EC during the six seconds metering is active.