Sorry for the millionth thread on the 24-70L. Anyways, I just got my 24-70L back from Canon where they adjusted the lens to the best focus point. I still have a couple of issues which I think are related:
1) On the tele end, the lens focuses pretty good, however, I am still having bad back-focus on the wide end. I have to either manually focus, or I have to lock focus at 70mm and then zoom back to 24mm to get a sharp shot at the wide end.
2) Also, another issue is when I look at the distance window on the lens, it never stays in the same spot when I focus on the same object on the wide end. It jumps around quite a bit but still always back focused. So shooting in the same condition can result in varying amount of back focused shots. On the tele end, it's fairly consistent.
I don't suspect it to be the 30D as the 70-200L F4 works perfectly and focuses fine in the same condition.
Now, I wouldn't care too much, but I recently started this exact test after I noticed many of my real world shots being back focused.
Please see pictures below for examples.
1st Picture: Controlled testing. 100% crop. The left image is badly back focused and the right shot is with me manually focusing it.
2nd Picture: Dog Shot: As you can see this was center focus on one shot. The image is at 24mm and is badly back focused.