Which is a better lens for the EOS R5? RF100-500mm vs EF 100-400mm

[Dmcd3055]

Which lens is better. 

Canon RF 100 - 500  F4.5-7.1L IS USM 

or 

Canon  EF 100-400mm f/4.5-5-5.6 L IS USM  with a 1.4x III

TIA 

[Danny]

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[Dmcd3055]

i currently own a 90 D and am getting an R5

[johnrmoyer]

I have not used any RF lenses. I use the EF100-400mm f/4.5-5.6L IS II USM +2x III a lot and even more often EF100-400mm f/4.5-5.6L IS II USM +1.4x III .

https://personal.canon.jp/product/camera/ef/extender-ef14-iii/spec 

https://personal.canon.jp/product/camera/rf/rf100-500-f45-71l/spec 

Carolina Chickadee (Poecile carolinensis) on Virginia Creeper (Parthenocissus quinquefolia) vine in Norman, Oklahoma, United States on March 28, 2024 ; EF100-400mm f/4.5-5.6L IS II USM +2x III

[Aurora4233]

Generically I will tell you I sent 14 EF lenses back to B&H after experiencing the RF difference (size, weight, focus speed etc etc etc).  I'm sure there are deep complicated debates about any and every RF/EF detail and you're asking a particularly interesting question by throwing an extender in there, but bottom line RF lenses have treated me exceptionally well and put the fun back into 'Funtography'!!  I've been a Canon shooter for 30 years and honestly couldn't believe the R/RF difference.

Move on to R/RF strongly and don't look back, you will not be disappointed!!!

[Tronhard · Accepted solution]

If you have decided to move across to the R5 and not use any DSLRs, then without doubt I would recommend getting the RF100-500 for the following reasons:
1. The RF100-500 is designed for the R platform and offers features that no EF lens can do, even if they are brilliant units for that platform.
2. The RF 100-500 has dual nano-USM motors that make its focus and tracking blazing fast, again something that cannot be matched by legacy lenses.
3. For wildlife you want as much reach as you can get, and obviously the 100-500 has better reach in its basic format.  Yes, you can strap on the 1.4x converter but you will lose a stop of light, and it adds an extra set of physical connections between your camera and the optic.  I have shot with the EF 1.4x MkIII extender, and it worked well but honestly it's not at the same level as the RF 100-500L and on an R5  you may well notice the difference.  The only other contender IMHO is the RF 200-800, if you can get one.

I actually still have the EF 100-400L MkII, it's a lovely lens, but since I went onto the R platform and compared it to the RF glass, I use it only when working with my last couple of DSLRs.