I am talking still photography sir. So rolling shutter?? "IQ reduced over mechanical shutter" I do not understand that. How can that be?
Imagine you have an EOS R and you are capturing a 3:2 video frame from the whole sensor and output it as a raw image (Which is way more taxing on the camera than Canon's 1.7x 4k 16:9 crop, as that one collects way less data in a more compressed format). That's how the electronic shutter works more or less.
Also with the R5 the camera needs to compress the 40+ MP raw files shot at 20fps, otherwise it fills up the buffer in no time.
It may even be a slight crop as well in 20fps mode, we don't know that.
But we know the 90D and M6 Mark II do have a silent raw burst mode, which crops in on the sensor slightly (but they only have the Digic 8 processor, not the Digic X, and 8k in the EOS R5 suggests the new sensor is quicker as well)
Luckily the compressed CR3 raw files show basically imperceptible degradation.
Inside Canon's new EOS M50 lies a new Raw format dubbed CR3, and with it, an option to record compact C-Raw files that are 30-40% smaller than their losslessly compressed CR2 equivalents. But what – if any – impact does that have on image quality for everyday shooting? Let's find out.
www.dpreview.com
But the bit depth will probably need to be reduced from 14-bit as well, so there is more noise in the shadows if you push them like crazy (which is unlikely in practise).
Everyone complaining about the 1DX III can understand now that with just 20MP, there is much less compromises for high-speed shooting, it can probably do 20fps 14-bit uncompressed, so no different compared to single shooting and the degradation with the electronic shutter is much less as well.
If you want to see graphs about how using the rolling shutter or the quickest burst modes can affect image quality with mirrorless cameras, check out
Jim Kasson's blog, he measured a lot of cameras, but no Canon cameras unfortunately.
Photographylife has another excellent article on the topic.
I've written everything down as clearly as possible. Basically, you switch your camera to silent burst mode, and you test the image quality (find the shutter speed where the banding is least prominent with the LED lights), and decide accordingly, whether to use it or not. Simple as that.
For instance, if you want to shoot street while walking, you will get a ton of rolling shutter in electronic shutter mode, while you are taking pictures, you need to keep the camera as still as possible, you move (meanwhile the buffer clears), and you hold the camera completely still again for a few moments, while the camera captures images silently, there may still be some artifacts, but way less when the camera is in motion.