I have a question regarding an other topic involving the R5 + RF 200-800mm. In this case not using a TC.
Recently during an excursion I/we had an encounter with a Red-footed Falcon. Initially we were not 100% sure about the identification, so we wanted proof.
The falcon was flying against the sky at quite some distance and flying in the direction from us. But I had no problem knowing where it was using my binoculars, so I knew I was pointing the camera in the correct direction and that the bird was there somewhere on the R5 screen.
The R5 had severe problems to get the bird in focus. I use back-button focusing and have copied the set-up that "Whistling Wings Photography" is using. I.e. Eye-AF using the whole field with one button, Eye-AF using Zone with the second button, and with the third button Spot-AF (no Eye-AF).
Trying all three buttons one at a time I still had these severe problem for the R5 to focus. I tried to focus at 200mm, 500mm and 800mm, same problem. Sometimes it would find the bird and for a moment the bird was possible to glimpse, but in a wink of time it was lost again. The end result: no sharp pictures of the falcon, some blurred pictures, and some where no bird was possible to see at all.
Have you or anybody else out there encountered a similar problem, and in such case do you have a solution?