Hi Jonathan,

I wonder if DoF may have played a role in what you are seeing, perhaps also a slightly different position of the owl and light. Just playing around with a DoF calculator, but 100 ft 500 f/7.1 would have a DoF of 5.13 ft and 100 ft 700 f/5.6 would have a DoF of 2.06 ft.

As for the numbers, a 1DX III with a 1.4 x TC is pretty equivalent to the R5, but slightly lower. Just using the 1.4x 5,472 x 3648 * 1.4 = 7,661 x 5,107 H, which is still a bit lower than the R5's 8,192 x 5,464. Throw in slight image degradation of the 1.4x TC (usually very minor) and the 1.4x really being more like 1.36x, and there is a difference, but I would expect it to require some serious pixel peeping to identify. Is this an extreme crop? Maybe it is enough to start seeing a difference in actual resolution?

If DoF is the issue, it would imply the 1DXIII set up missed focus a bit.