I am using it with R5 and it works absolutely wonders. It's so fast, it's so sharp and both with the 1.4 TC engaged. Amazing lens for wildlife, zoo, bird photography, perfect universal setup. It's essential however to setup and adjust the AF menu section properly for bird photography. Most of the birds I shot recently in Ecuador I used TC = f5.6 and with R5 after cropping, thanks to the 45 mpx sensor, the results are amazing.
Been using the 200-400 f4 for years with 1dx range and now the R3 and R5 mkii and it works perfectly for sports. Sharp as a pin and fast autofocus. I shoot handheld all the time, although it's not easy to hold steady for long durations.
I recently got the 200-400/4 and I use the R7 and so far its fine. If I encounter any focus issues I can always slow the burst rate or put on my 0.71 for more light! I’m contemplating the R5ii/R3/R6ii but not in any rush so I can wait till the time is right as there might be a new R6iii at some point and who knows what’s going on with the R3 if we will have a replacement.l (and 45mp is my cup of tea) Canon have a firmware update for the 200/400/4 so do apply it particularly if you would benefit from the improvements. The 100-400L II is lovely too, just depends what tool one uses but there is a stop of light less with this one
Using R5 and R7. For birds almost exckusively the R7 with a RF 200-800. I considered buying this one for more light. But since I would use it with the R7, I'm not sure anymore. The reach with my R5 wouldn't be enough for me.
I have set my R7 autofocus reaction settings down one notch and find it works well with my EF 500 mk1. I don’t buy the battery argument. It is more likely to do with the sensor and AF detection abilities of that sensor. Or some decision Canon made… but as an engineer working on stuff like this for a living I can tell you the battery argument is BS. You are right though - the R7 works flawlessly with the EF 100-400 ii, but to me, it looks like it hunts somewhat on the EF 500 i, and by tuning down the reaction it seems to do so less… or I convinced myself that it does!
I see in the comments below that many remark that the lens is very sharp. Some internet attention seekers claim this lens goes softer with age? I can’t see why. Any comments from owners regarding this? I am interested in getting a used copy at some point
