I too have been having problems with focusing lately, here is my story; I sold my medium format / digital back system because I was not having much luck manual focusing, I think my eyes are going bad. I have been shooting the Canon 1Dsmk3 and was noticing that certain lenses were front focusing, about 5 feet in front of the subject when the subject was at least 20 feet from the camera, and other similiar situations. It never seemed to happen when I was relatively close to the subject. It was only happening with my 300 F4 L and 85 1.2 L lens and 100 F2 non-L lens. My 50mm 1.4 non L seems to be work fine.
I called canon support and had them walk me thru the micro-adjustments procedure, seemed to help a little bit but not really sure. Thats the problem, the front-focusing problem is not consistent. I called canon again, we did the lens test on the phone, I emailed him jpgs of a ruler shot at a 45 degree angle, everything checked out fine.
Then he said this, which surprised me, " for best results use the CENTER only AF focus point and recompose once you get focus. Do not use the other surrounding AF points, those are only for al servo mode when tracking a moving subject. Really? They told me that yesterday, I shot today with his advice and he seems to be right, I nailed focus more often than not, but it is too soon to tell.
Has anyone else heard this? I was thinking of sending all my lenses and camera body to canon to be checked out just to be sure there isnt an actual problem, but I would prefer not to obviously.
Just to re-iterate; the main focus problem seems happen when I am at least 20 feet away from the subject, and after focusing and recomposing from a non-centered AF point the camera places the focus a few feet front of where I focused.