I have been wanting to test out my new R3 for some sports shots. I went out and shot a High School football game to put it through its paces. Shot in Shutter priority with Auto ISO. I started off the AF tracking on to see how it performed. I also wanted to see the ISO capabilities as well. My last Canon body, 1DX, was stellar at the time I bought it but was looking forward to see how the R3 stacked up. The AF tracking worked superbly with my old 400mm with the adapter. In the second half I turned it off to center point focus to see the differences. For me there wasn't much of a difference because I shoot differently as I wait to see where the ball is going then grab focus. Both seemed fine in their applications. The ISO performance was amazing. Shot a few as high as 25600 to see what it could do. I do believe that the highest you can go to preserve a really nice image is 12500. I ran a few of these images through Topaz. I tried to leave a bit of noise to preserve sharpness. I was trying to shoot at a minimum of 1600 of a second. I plan on shooting again and knowing what I know now, i'm sure I will use Shutter priority and stay around 1250th of a second to keep the ISO around 8000.
Thanks for looking.
Joel

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/3.2 1/3200s 1000 ISO 0.0 EV

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/2.8 1/1600s 6400 ISO 0.0 EV

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/3.2 1/1600s 10000 ISO 0.0 EV

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/2.8 1/3200s 25600 ISO 0.0 EV

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/3.2 1/3200s 25600 ISO 0.0 EV

Canon EOS R3 EF400mm f/2.8L IS USM lens 400mm f/2.8 1/1600s 200 ISO 0.0 EV