Ja, itt szépen le is írják, hogy nincs f/8-nál AF, bár a második kérdésnél kitér a válasszal, szerintem ez a "még belekönyöröghetitek a következő firmware-el" esete...

"DB: Everyone is very excited about the new AF system in the EOS-1 Dx.  Among wildlife photographers, the big concern is the loss of f/8 autofocus.  Why did Canon choose to eliminate that feature?
CW: Canon felt that while it would have been nice to preserve AF at f/8, the overall improvement in AF achieved with the 1D x took precedence.  The new AF system is faster, more controllable, and more intelligent.  The improved algorithm means that AF won’t jump to the background as quickly, won’t be tripped up as easily by obstacles in front of the subject, and will handle subjects that are small in the frame much better.  As you mention, AF is unavailable on the EOS-1D X if the maximum aperture reported to the camera through the electronic lens mount is smaller than f/5.6. This is a lower specification than previous EOS-1 series DSLRs. There are a lot of trade-offs in life, and this is one of them. Essentially, Canon Inc. decided that the overall improvement of the new 61-point AF system compared to the older 45-point system took precedence over the need for that particular feature. Taking your f/4 lenses as an example, with the new 1D X you now have 41 cross-type AF points (or 21 cross-types with the f/5.6 lenses) plus color and face detection tracking when using those lenses whereas there were none of those features with previous 1D/1Ds cameras. The AI Servo system on the new camera is vastly better than earlier cameras as well, in terms of sensitivity and performance as well as controlability.

DB: Does that mean that it’s not possible to AF at f/8, or that it’s not reliable but could be implemented?  Could f/8 AF be enabled as a custom function?
CW: I have no further comment at this time, because Canon Inc. has not published answers to those questions."