R5 @ 500 mm versus 1DXIII @ 700 mm

[HDNitehawk]

The test would be the 500mm with an adapter on the R5 and the 1DX III without.
You sure it isn't the difference in resolution that you are noticing?
I was looking at other points in the picture and comparing, like the tree.
500mm at f/7.1 versus 700mm f/5.6 different DOF and that can be an issue.

The 100-500mm shot isn't to shabby at all. The owl looks good. If you had the R5 with its higher resolution and the 500mm F/4 and a lower aperture could it have improved.

I have the 100-500mm and really haven't played with it much yet. I need to get it out and give it a good test drive.

I am starting to arrive at an opinion on the R5 and it isn't in line with many of the great things I hear. First I can notice the difference in resolution from the 5DsR even though it is slight. The AF of the R5 is not on par with even my old 1D IV for the tough shooting and finding targets when hunting. The eye tracking is great, the flippy screen is great and in general it focuses really well. It is more convenient to get shots when you don't have to have the camera on your face. Last night I went to my sons wedding and took the R5 and used the 35mm F/1.4. He had a photographer but I wanted a few shots from my perspective and a few shots with that special Bokeh you can get when shooting at f/1.6. Generally shooting almost wide open is tough for the DSLR's and I have to say my keeper rate was really no better than I would have gotten with the 5DsR. There were several sets it didn't achieve focus as it should.

I am waiting on Canon to bring out a R1 that they believe has an AF equal to the 1D series.

[Kayaker72]

First I can notice the difference in resolution from the 5DsR even though it is slight.

Yep. While I have never shot the 5DsR, here they are carefully compared and they came to the same conclusion.