As you probably saw with my Image of the Week submission, I played with my new RF100-500 on the R5 yesterday and had quite a bit of fun. I really wanted to test the auto focus capability with birds and especially birds in flight. My subject was Great Grey Owls, and we had plenty of action. At this point I would rate the focus performance as "pretty good", and I'm especially hoping that I can get some feedback as to what might have been going wrong in some cases. Have a look at the sequence below and please share your thoughts.
My focus settings were:
- Servo, animals, eye-detect enabled
- AF mode 1, with tracking sensitivity set to -2 and accel/decel tracking set to +2 (I heard this was supposed to make things better)
- All focus points activated, with the initial point chosen automatically
The focal length was at 500 mm, aperture f/7.1 (wide open). Images below are unprocessed and not cropped. I used electronic shutter at 20 fps.
The conditions were obviously challenging for focus. A long-distance shot, a busy background, and plenty of snow falling. The camera had the owl in focus before it took off, but could then only hold focus for a couple more shots before it lost it completely. The images after this sequence are progressively worse even though I held the owl close to the middle of the frame.

#1: Sharp

#2: Still good.

#3: Still good, but really hasn't moved much yet.

#4: A bit of softness

#5: Completely soft

#6: Lost it completely, focus shifting to the background

So what do you think? Is it the distance, the tough conditions, wrong settings? Or some combo of all that? I'd appreciate your feedback.

You can click on any shot to see a larger version.