I recently took some photos for a friend in a very brightly lit environment. The images were using a 24-70L with my 50D and of a sunlight wall with my friend leaning against it. The camera was on AV priority at f/2.8 (accidentally, I must admit). As a result, shutter speeds were in the order of 1/2500. I'm also very careful with holding a steady hand.

Because my friend was right of centre in the images, I used one of the off-centre focus points.

Every photo was slightly out of focus. As I scan the wall and the ground, I realise that no part of the image is in focus. So it doesn't seem to be a front or back focus issue. The fast shutter speed means it shouldn't be motion blur.

I can't work out why these images didn't work (well they do, just not when scrutinised at pixel level).

Could it be:
- using one of the diagonal focus points?
- shooting wide-open in conditions that are too bright?
- Anything else?

Any comments appreciated.