40D & f/2.8 Conundrum

So... If lens is a bit soft at f/2.8, send it back ?

let's all be nice

I'm California-n, not Canadian, and I think I understand the original authors question as well.

You'd mentioned research, and I wonder if you've seen the auto-focus explanation on FM:
http://www.fredmiranda​.com/forum/topic2/2415​24

There is mention in the article that lenses f2.8 and faster have tighter tolerances (1/3rd the depth of field) than those slower (anywhere in the DOF), which would ultimately lead to sharper images.

My rudimentary understanding of autofocus systems have been that they look for the best available, rather than absolute, difference in contrast. The result being that while an f2.8 lens might be softer than the f4 in absolute terms, the autofocus will still be effective since it can deduce what it perceives as sharpest (and going back to an earlier posters mention of racking the diopter back and forth -- though the FM posting says it doesn't zero in).

anotherbrian,
Great article. It sounds like it's for a different camera, one with outer points being single and a center cross-type (with fast lenses), whereas the 40D has outer points being cross-type and the center being diagional, again with fast lenses.

I'm not complaining. It's easy to extrapulate the information to the 40D's AF set up. Thank you so much for the information and the well-worded answer to the question I asked.

Are you sure you're not from Canada?