There has been a lot of debate out there about the performance of the R7 autofocus, and especially eye tracking, with third party lenses, specifically the Sigma 150-600 Contemporary. There have been claims of pulsing, but Sigma recently put out a short video claiming their lenses work seamlessly with the R bodies. However, they were using the FF R6 and not the R7. I personally had no issue using the Sigma 150-600c and 60-600s units, but I was using FF sensor cameras and that is, I believe, significant.
I have shot wildlife most of my life and, like you, I have (amongst others) the Sigma 150-600c and Canon 100-400MkII. I deliberately chose to go to the FF R5 and R6 bodies rather than the R7 for the following reasons:
While the R7 claims to have a high shutter rate of 30 FPS in full electronic mode, this causes issues of image recording, throughput and storage. This is because, to me, the data bus is seriously unbalanced.
What I mean by that is that the shutter can go at 30 FPS in full electronic mode, but because the sensor is not BSI/Stacked, it's ability to process the recording of the image introduces significant rolling shutter effect, where a bird's wings in flight will look curved rather than natural because as the sensor scans down to record, the speed is not sufficient to compensate for the movement of the wings' displacement. This is also seen when tracking birds in flight, where trees, poles and buildings will look tilted or round objects will look elliptical. Now, this is obviously not an issue if the birds are relatively static, but then one would ask why it is necessary to shoot at 30fps for a bird that's not moving.
The second implication of this is that the buffer is insufficient in capacity and speed for the readout. This means that at 30 FPS the buffer will fill up in about 1.2 seconds, and then you can't take any photos. This is also due, in part, to the relatively slow cards - I would have preferred to see at least one CF-Express card to allow for the fast recording speed.
The 32MP sensor of the R7's APS-C sensor has a pixel density equivalent to about 82MP on a FF sensor. As such, it starts to exhibit noise from about 3200 ISO, becoming noticeable at about 6400. Furthermore, given that the R7 has a version of the tracking system designed for the R3, which has a FF 23MP camera, I am dubious that because the sensor is so critical in the focusing and tracking processes, the autofocus is challenged and that may be a part of the reason that several people have had issues with focusing and tracking. I will say that the system is much more sophisticated than those of DSLRs and thus requires more study to configure and use. To be fair, I think that quite a bit of the negative feedback is from those who have not set up their systems to make the best of the technology for their specific needs.
The R7 is not weather sealed like the 7D series bodies, nor does it have a battery grip - something that I really prefer with long telephotos, for the extra energy capacity, but more for the balance and the duplicate controls for shooting in portrait mode when using big leavy lenses. Again, those are my preferences and may not be relevant for you.
These were MY reasons for not going for the R7, much as I was looking forward to the release of the new body. You must decide for yourself, based on your own style, subject type and circumstances, but I would recommend quite a bit of research before you make a decision.
Much depends on what you are going to produce. I don't generate large, detailed prints any more, so the 20-24 MP range for the FF bodies works fine for me, and if I really want to crop to fill the frame, the R5 can do that in 1.3 or 1.6 crop down to a minimum of 18MP, which is enough for my purposes.
As Demetrius said, if the 30FPS is the big draw for you, you would need to go for RF native lenses like the RF 100-100 STM or the 100-500L USM lenses. Using legacy lenses sets you back to about 12FPS, which is mechanical shutter territory and avoids many of the issues I outlined for electronic shutter but again, from what you post, that high shutter speed is something you see as a benefit.
I shoot mechanical and still get images that I am happy with for both static and on the wing subjects. So, I can quite happily work with the R5 and R6 bodies that are weather sealed, have grips, solid tracking and sensors that handle high ISO, if I need it.
cheers, TREVOR
Before you ask us, have you looked in the manual or on the Canon Support Site?
"All the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
