RF 135 f/1.8

[Kayaker72]

Thank you for the explanation, I had no knowledge of the physical limitation. I was out of the game for over 5 years. I heard EF lenses work better on mirrorless than they would on DSLR, is this true?

Well you don't have to do any AF microadjustment with lenses on mirrorless cameras, and there is some improvement in stabilization due to the IBIS working with the lens IS. Otherwise I'm not sure what the differences might be. Maybe the focusing is faster? I would be surprised if that were true.

I would say that EF lenses work remarkably well on my R5.

Better? No, I wouldn't say the lenses are better on RF mounts.

I think there are advances to recent bodies and that those bodies happen to be mirrorless. But, then you are really getting into a discussion about 2020 or more recent technology that received a lot of investment vs 2016 (going with 5DIV for a date) technology that Canon wasn't necessarily investing in as much (my speculation).

The cameras can do more. Just to add to Jonathan's list: AF spread, AF-eye detect, level/histogram in EVF, more fps, less interference with AF due to mirror movement, ability to shoot 1.6 crop, customization of buttons, etc.

But I never want it to get lost, the image quality is primarily a function of the lens was great on DSLRs. If a mirrorless body improves that, I think it is mostly due to generational improvements to filters/sensors/processors and not the lens itself.

[Fast Glass]

The cameras can do more. Just to add to Jonathan's list: AF spread, AF-eye detect, level/histogram in EVF, more fps, less interference with AF due to mirror movement, ability to shoot 1.6 crop, customization of buttons, etc.

Not to take away from what you said, but the 5Ds could also do 1.6 crop modes. Which is a bit of a misnomer because it doesn't really crop anything and just basically a guide for you to crop in post, if shooting RAW. Which I don't really find super helpful, unless you want to shoot 1.6 crop lenses. But would anyone really do it? Probably not many.

If it gained me a smaller file size for more buffer, faster FPS, 14 bit instead of 12 (A caveat with shooting 20fps on the R5 or R6) then yeah. I could see myself using it, but if I'm still managing full rez images regardless. Not super useful to me.