Trouble with exposure using aperture priority

[ChadS]

@Neuro's suggestion I pulled all the EXIF data with exiftool (handy utility that). There are many difference between shots, obviously, but two discrepancies that I cannot explain (just looking at two photos, let's assume that pattern holds)

In the overexposed shot I have:
AE Setting: AE Lock
Raw Measured RGGB: 0 0 0 0

For the properly-exposed shot I have
Raw Measured RGGB: 142716 283278 285415 128586
and I have no entry for AE setting.

I have no idea why the Raw Measured RGGB data is all null for the overexposed shot but the AE lock does tell me what the problem with that exposure is. However (and I just tested this and it work properly) one must hold down the AE lock button between shto carry the exposure through multiple shots. While I might have accidentally pressed this button I'm certain I did not hold it down for those three shots. I'm guessing that microswitch is sticky.

At least I know what to do to get out of that problem now. Thanks for the suggestions folks.

[ChadS]

On a totally different topic, a 200mm lens just isn't long enough to get a profile portrait of even the most mild-mannered birds even on a 1.6x crop body. This is the best shot I could manage - from about 20 feet away. Yes, the framing stinks. I'd crop if if I were going to keep it. but those darned birds bob and weave as they walk.

[ChadS]

So the camera decided it wanted to fire the flash, fired it but didn't pop up? Yet the picture is over exposed not under exposed. I always hated the pop up flash on the 50d and 7d, they always wanted to pop up when you didn't want them. I would update the firmware, check all the settings in the camera and possibly return the settings to default and see if you can still replicate the fault.

I've never seen my flash popup in manual or aperture priority. Is that possibly on the 50D, 7D?

[HDNitehawk]

I've never seen my flash popup in manual or aperture priority. Is that possibly on the 50D, 7D?

Maybe not, maybe all this time it was me hitting the pop up button and thinking the camera did it. Doh... I haven't had the 7D in over a year and even then I didn't use the inboard flash I used speed lights.

I would still change the firmware and settings. Couldn't your problem as likely be a firmware glitch as a mechanical one?

[Positron]

So the camera decided it wanted to fire the flash, fired it but didn't pop up? Yet the picture is over exposed not under exposed. I always hated the pop up flash on the 50d and 7d, they always wanted to pop up when you didn't want them. I would update the firmware, check all the settings in the camera and possibly return the settings to default and see if you can still replicate the fault.

I think Neuro was suggesting that since the max flash sync on the T2i is 1/200, if it decided it wanted to fire the flash, it would do everything in its power to keep the shutter speed under that, which it may have felt possible at f/5.6, but not f/4.

Personally, on my T2i, I've noticed that in bright daylight when there is bright, reflective white in the frame (like on that bird) it has a nasty tendency to screw up the exposure (usually underexposed, but not always). Judging by the shadows, it looks like the sun is directly overhead, so the contrast of the incredibly bright white feathers against a background that would be pretty dramatically underexposed may have thrown it off, if you metered across the frame. Personally, I find it faster to just go into manual mode when I find myself shooting in situations like that, although flicking exposure compensation can be quicker if the failure to properly expose has a regular pattern to it.

[ChadS]

@Positron see above - turns out the trouble was that my camera was under the impression the AE Lock buttons was being depressed (which I would have noticed doing for 3 shots in a row). Clearly there's something wrong with that button (or the camera's firmware, true). Turning the wheel to change apertures must have 'unstuck' the button either electronically or in the firmware.

[Positron]

Ah. Somehow I missed that. Glad you got it figured out.