Canon 50mm 1.4 focus issues

I'm a little fuzzy on the way back-button AF works on the 5D2. Do you know that AF-on will lock focus in this way in AI servo with the settings you have? You might think of some way to test this with your camera. If you lock focus on something close by and then turn the camera on something else far away and take a picture should prove the point. If the new subject is out of focus it would imply that focus lock did happen. You can probably figure out other tests to do.

If you are locking focus in this way, then your issue may just be due to the focus-recompose geometry issue I mentioned. The usual fix for this is to use the outer focus points to focus with, but those don't work all that well with the 5D2.

You might try the focus no-recompose method for awhile (compose by cropping) just as a test to see if that is the root of the problem.

Your settings show that you do have center point auto expansion enabled, so there is a chance that the focus point is not quite where you think it is. It may have strayed over to one of the expanded points. It may be worth playing with that setting to see if it has an effect on your problem. It is a useful setting for tracking subjects that are moving, but may complicate your AI servo focus recompose method.

You might also try one-shot for these kind of shots, just to see what effect that has. I use AI servo on static subjects with the 5D3 without many problems. However, I don't focus-recompose while doing that. I will either focus using outer points or compose by cropping (or a combination of the two).

Anyway, I'm about out of ideas. Study up, experiment, and let us know what you figure out. Or maybe someone else that is more familiar with the 5D2 can advise. It is hard to believe I have forgotten so much about the 5D2 in just one year.
--
- Bill