I found a sleepy owl in a tree today, so I had time to take a variety of shots. I used the R5 with the spiffy 100-500 lens handheld, and then I set up my 1DXIII with the 500 f/4 and 1.4 TC on a tripod to get a bit more reach and take advantage of the wider aperture. When I looked at the results at home, I was rather stunned to see how much sharper the images are from the R5. Is this camera and lens combo really that good? Here are a couple examples, both cropped to about the same dimension. Neither image is post-processed at all.

From the R5: 1/2000 sec @ f/7.1, ISO 1600 (I was using a fast shutter speed in case it decided to fly)

From the 1DXIII: 1/800 sec @ f/5.6, ISO 320

Maybe it's a focus calibration issue? Or the different aperture? I really thought my 1DXIII was sharper than that, but I don't use the 1.4 TC all that often. I wish now that I had brought my RF lens adapter, then I could have tried the R5 on the same setup to see the difference.

But really, I'm becoming incredibly impressed with what the R5 can do. Even when connected to a 500 mm lens, I can get better results than I can with the 1DXIII at 700 mm.