I tried taking some BIF pictures with a 5DIV, 600mm V2 & 1.4 Ext V3 on a tripod mounted gimbal. I used AI Servo AF with Zone AF (9 point with center) with Case 2 (I tried other cases, but 2 seemed the best). I found the AF had trouble locking on to the birds, particularly when they were low with a background of long grass or trees. It worked better when the background was sky, but it did still lose focus fairly easily and I'm not convinced the AF could keep up with the movement. I think it was locked on for the pictures I have attached, but it may not have been at the instance of the exposure. I estimate the owls were about 150 meters away. The pictures have all been cropped to 2400px X 3600px @ 300dpi, with file sizes ranging from 1.25MB to 1.81MB, but I don't know if this site changes that on the upload. The first picture was taken at f5.6, 1/1600 sec & ISO 250 with +.67 EC. The last 2 were at f8, 1/2000 sec & ISO 640 with +.67EC. None of them look particularly sharp to me. What I'd like to know from others that use this combination of equipment is whether it is possible to get significantly better sharpness or is this about the best I can expect given the equipment and distance involved. Perhaps there just aren't enough pixels on the owls. From the top of the heads to the end of the claws is about 470 pixels.