Let me start with this - I really had big hope that the EOS R would perform well as I was looking for a Camera that would be smaller than my other Cameras (1DX MK2 and EOS 5d mk4) with a flip screen or even a tilt screen for pictures or video closer to the ground and offers USB Charging.
Yes some of you will already raise the hands here and say USB Charging on the EOS R is not real USB if you need a special Charger and I need to agree - not a good solution offered by Canon here! But due to the small size of the Batteries and available USB charging stations for these batteries I would find a workaround for me.
Just a side note : I bought a Sony 7r3 some month ago to play around with and must say not bad but the major problem with adapting Canon Lenses is the Auto focus especially over 300 mm regardless if it is a fix focal lens or a Telezoom. The performance of the Sony is not too bad on single shot but on continues AF it simply not fully usable for wildlife.
OK back to the EOS R and what I was expecting:
Build Quality/Weather Sealing is on the high standards of Canon
Picture Quality is on the level like the EOS 5d mk4
Electronic View Finder would work great
AF should perform close or at most slightly slower to my EOS 5d mk4 on all Canon EF Prime lenses!
Very good AF in critical light as promoted by Canon with -5 stops what would be great to have!
Compatibility with non Canon Lenses might be not on the same level like with Canon original Lenses
New "creative Touchbar" and Display to change focus points not really ideal for Wildlife especially not if you wearing gloves but maybe good for normal use!
I would say not too high expectations and yes only one card slot but I must say I normally only use one and save the card on external devices and keep the card as the backup.
So how did the EOS R perform ... Not good and I will tell you why!
Build and Picture quality I really enjoyed - solid build and you have a good feeling if you have it in your hands. Also the Picture quality is at least as good as the EOS 5D mk4 what I am very happy with and the EVF performed really good. But these are my only positive points I can mention here.
Already in the beginning of the test I was not too happy with the AF performance just a feeling - slower than my DSLRs, not as reliable . In wildlife you have only a limited time or chance to get the photo you are after and I really talking seconds some times a animal is visible or at the right location so you need to focus fast and will normally use back buttom focussing and AF Servo mode if the animal moves.
I tested the EOS R in a Park nearby where you have quite good or even would call it controlled conditions - much easier than a real wildlife situation. I tested the EOS R with the EF100-400 Version 2 and with the Tamron 150-600 G2 you remember I was searching for a small combo! I also have a few other lenses like the EF200-400 1.4 or the EF 500 F4 which I also tested briefly with the EOS R.
As long the conditions are super good - bright sun or very good light animal standing in a free spot the AF was OK not super great but OK. Touchbar for changing AF mode worked OK but the Display to reposition the AF field while using the Electronic View Finder was simply a pain. Even when you select only the upper right part of the Display to change AF your thumb need to travel a lot and a long way back to the (in my opinion) wrong positioned AF-on button on the back. The AF button is far to right so simply not really a relaxing position to start AF or track animals while they moving. The other fact in Wildlife photography is that the highest chances of getting a good picture is best in most of the cases around sunrise or sunset and here clearly the EOS R performs too bad for me.
Following the first example:
EOS R with the Canon EF100-400 v2 at 125/sec 371mm f5,6 ISO2000
EOS R with the 100-400 v2 at 125/sec 312mm f6,3 ISO3200
In my view and also for all my cameras I own a super easy setup for a camera - an animal (in this case a chamois) standing still, very big distance between the animal and the background in still OK light conditions ... and the result and I tested the Canon EF 100-400 v2 and the Tamron 150-600 G2? The EOS R was hunting for several seconds to find focus if at all. I was so shocked that I double checked all settings again and again - adjusted AF response and all settings which could have an impact but no real improvement. Here we come back to the side note from the beginning about the Sony 7r3 hope you remember that AF Performance is getting worst over 200-300mm or so ... yes this was the problem also the EOS R was dealing with. When I zoomed out to less than 200mm the AF was performing slow but OK again.
EOS R with the 100-400 v2 at 125/sec 163mm f6,3 ISO2000
OK time for changing the drive and test single shot but also here very bad performance over 250 mm regardless of the lens. Maybe some of you would assume that the Auto focus was maybe hitting the Background or so - no sorry simply hunting several seconds before it found something to Focus on sometimes the Background sometimes the Chamois. I even tried to focus on the Rocks below the Chamois but even here same results as described. This is the main reason for my harsh title of this Blog Post and my conclusion that this Camera is not performing as promoted.
The following 2nd example is something maybe a lot of people do not care about too much but as I really like backlit shots it is important to me.
EOS R with the Tamron 150-600 g2 - 1/800 at 428mm f6,3 ISO800 - 3 exposure / with Photoshop adjustments on Brightness and Contrast as -3 exposure was not enough to get a full black background.
You can only underexpose of 3 Stops what sometimes is not enough to keep the background black if you want. With the DSLRs you also see only 3 Stops over or under exposure on the display but you can go lower so you have the freedom to create the shot you are after without doing some "bigger" adjustments in Photoshop or so later on. I always try to get the shot I am after in the camera but also I use Photoshop or Lightroom for adjustments - just for the records.
Final Comment - I double checked all settings multiple times and even done some test at home and the results where on the same level - OK performance at high contrast scenarios - but if the light start fading away at longer focal distance the AF is not usable for wildlife photography! This is my personal opinion and would suggest you do your own test!
Hope this helps you on and let me know if you have different findings (but please in similar conditions not like a runner with a red and blue shirt is running at a bright day :) )