May i know on what basis your opinion was formed about AF of A1 compared to R3,R5 & R6.Did you compare them by shooting side by side ? I am curious since i am planning to buy A1
1) I tested R6/100-400 & A9/200-600.
While R6 tracked swallows in flight in bad light easily even with a busy background, A9/200-600 couldn't. A9 kept focusing on the background.
Canon's AF at the moment is way superior, IMO.
When I say AF, I mean both tracking & initial target acquisition.
Speed of initial target acquisition.
(Amongst the 3)
1st place - Canon R6/100-400 usm ii
2nd - D500 with 500pf
3rd - A9 & 200-600 (wasn't good)
It is important to note that only A1 has a dedicated bird eye tracking. It is a new software that Sony is still trying to improve, while Canon's general purpose animal AF is excellent for bird tracking too. R6 was excellent. So it is more software than stacked sensor readout speed.
A pro YouTuber/photographer also spoke about how he got a swallow in flight shot with A1 & 600 f4 by pre focussing...
IMO, you don't need to do that for Canon as the AI is that clever...
2) All the YouTube reviews indicate that R5/R6/R3 AF is either equal or better than Sony AF.
3) If I were you, I would still pick A1 over Canon, as Canon sensors are not great. Also, Sony AF can get better with firmware updates.
4) Anyway, don't take my word for it. You should definitely try the different bodies before buying them. You should share your experiences after you test them. I would love to know.