Is the 5d mkii focusing better or worse than the 40d for birds in flight? I understand that the center point is more accurate, but is it faster than the 40d? I only shoot birds about 25% of the time, I use for BIF a canon ef 400mm L f5.6 and for stationary birds an old Heinz Kilfitt 400mm f4.0 manual focus lens as well. The other 75% of the time I know the 5d mkii would fit me perfectly.The lens is the major factor for speed of autofocus, while the body controls the ability to track and accuracy.
I am happy with my focusing on the 40d with the smaller aperture (f8.0-f11.0) required for birding. As long as it is at par I will be happy.
I understand that the 1dx 1dmkiv and 5d mkiii are better cameras. I have just installed a new furnace new air conditioning and have completed a basement reno(aka I have no cash flow), I am finding the cheap price of the 5d mkii very tempting, And I would like to know if anyone else has made the switch from the 40d?
I would not recommend the 5D Mark II for tracking moving objects as they moved to the different AF points. It is certainly quite accurate in the center point and will focus quickly.
Why not move to a 7D? Much more usable AF for BIF, and for $1087.20 in the Canon refurb store (sale ends today), its a good value.