m1mm1m
My only comment is, that's not the most challenging BIF, but it is a positive. There are some evaluations out there that consider the AF with longer lenses, possibly in slightly lower light, to be rather unacceptable, so more clarification/examples would be most welcome since I'm on the fence regarding buying the R.
Jack
Absolutely without a doubt landing pelican images are very far from the most challenging BIF photography.... LOL... Also without a doubt, the "R" is not the optimal BIF camera even with a "proper" BIF lens and no TC. While AF is quick and excellent (as good as XYZ) with a fast lens, no TC, in decent light, and you do get AF all over the sensor, you are still hobbled by the 5fps frame rate. For very fast subjects, the 7D2 eats it alive and even more so, the 1DX2. I have both and would not give up either for an "R" a this point.
My only point was to illustrate that on the "R", AF works sensor-wide with any lens/TC combination at any aperture and it works acceptably enough to even use for some BIF. On most high-end dSLRs, you get center spot from 5.6 to 8 and nothing past 8..... This is way better. For static subjects, AF even at tiny apertures is as accurate as the R's AF ever is... IOW, very.
If having acceptable AF capability at small apertures matters to you at some level..... I would certainly consider it for that as well as it's other attributes. Personally I have 4 issues with the "R" Canon would need to solve before I spend money on this. See my previous posts for what they are. Yes, my current dSLRs are heavier and bigger, but they do what I need done better than the "R" at this point in time and I can live without AF at small apertures.