yep, that's almost certainly what's going on. Unfortunately the 40D doesn't have the micro-adjustment feature so we're kind of stuck; calibrate your most-used lens and take your chances with the rest of your kit, or compensate using MF. Obviously it'll depend on how bad your images are.


My 40D/50 1.4 combo is the only one that has an issue so I generally MF with this lens. As you'd expect it's not my first choice for action shots! But with practice I've gotten pretty good, pretty fast getting a sharp image.


I know many folks swear by the AF-S screen as a replacement for the original focusing screen in the 40D. My experience with it was a disappointment; in fact I notice no difference at all. Honestly I think somebody slipped the wrong screen in the box.


Anyway, if it comes to MF for you, give the AF-S screen a try. Most of the reviews of it are positive. It's only about $40 and if you buy it from B&H you can return it for a full refund if it doesn't perform the way you expect.


Best of luck!