On an R body this is NOT the lens to buy :(

With the adapter the weight is near twice the weight of the RF 100-400, is 3 times the price $1400+ $100 compared to $500. The 70-300 is a bit shorter but thicker at 2.5 lbs with adapter while the 100-400 at 1.4 lbs. The 70-300 is 1 stop faster and the 100-400 is 100mm longer. The IQ is about the same. YES I did own one for my EF mount bodies. The usable ISO range on a R5 and R6 body is at least a full stop better. Plus dont plan on using an extender with it. The only extender that I know that works with it even on a EF body is the Kenko HDpro 1.4x and 2.0X but the catch is they wont mount on the RF adapter I still have both gathering dust

YES I know this is the EF forum when but you make the move to R bodies you may think back to this

RF extenders should work though. All you need is modified RF to EF adapter. The downside is that the extender will be invisible to camera: EXIF will be wrong and you have to think about your aperture settings. IBIS is likely not as efficient as it could be.

A really good lens however.  I own the EF 70-300L.  Not sure how the image quality would compare side by side with the RF 100-400

lol

S Castle wrote:

davel33 wrote:

YES I know this is the EF forum when but you make the move to R bodies you may think back to this

Why do you think this forum is for EF lenses only? The title is "Canon SLR Lens Talk". There's no "D", so all Canon SLR lenses are up for discussion.

Indeed. However, the "R" in SLR stands for reflex, which implies mirror.

I have this lens, and was expecting to read that it performs poorly on mirrorless. But no. It's an excellent lens, and all you seem to be saying is that with the adaptor it's heavier. Also that it doesn't accept most extenders. I knew that.

The EF L zoom very likely has superior optics. That and the extra stop makes it a very good competitor to the RF 100-400.

J.K.T. wrote:

S Castle wrote:

davel33 wrote:

YES I know this is the EF forum when but you make the move to R bodies you may think back to this

Why do you think this forum is for EF lenses only? The title is "Canon SLR Lens Talk". There's no "D", so all Canon SLR lenses are up for discussion.

Indeed. However, the "R" in SLR stands for reflex, which implies mirror.

Perhaps the R in the forum name is overloaded to mean mirror when discussing EF lenses and R series when discussing RF lenses.

bodeswell wrote:

J.K.T. wrote:

S Castle wrote:

davel33 wrote:

YES I know this is the EF forum when but you make the move to R bodies you may think back to this

Why do you think this forum is for EF lenses only? The title is "Canon SLR Lens Talk". There's no "D", so all Canon SLR lenses are up for discussion.

Indeed. However, the "R" in SLR stands for reflex, which implies mirror.

Perhaps the R in the forum name is overloaded to mean mirror when discussing EF lenses and R series when discussing RF lenses.

And perhaps the "R" could mean Rainbow

You got the problem the wrong way around. I had constant trouble getting reliable focus  with my EOS R and EF 70-300L. I got rid of the dreadful EOS R and replaced it with another SLR and all was well.

Tannin wrote:

You got the problem the wrong way around. I had constant trouble getting reliable focus with my EOS R and EF 70-300L. I got rid of the dreadful EOS R and replaced it with another SLR and all was well.

It does seem like you supported my post with your story, thank you

I loved using my 70-300L on my old 5D3/4, then my M50 and its on my R7 most of the time.

No issues at all. Any weight or balance issues are just a case of getting used to it.

dave_bass5 wrote:

Any weight or balance issues are just a case of getting used to it.

I disagree with your statement, its not getting used to it, its putting up with it.

davel33 wrote:

dave_bass5 wrote:

Any weight or balance issues are just a case of getting used to it.

I disagree with your statement, its not getting used to it, its putting up with it.

All this body-lens "balance" thing is fully artificial issue. When holding the combo properly, right hand carries only a small fraction of the whole weight. Left hand supports majority of the weight by supporting lens from below in the center of balance of the combo. Potential front/back imbalance of the combo is solved by moving the left hand forward/backward on the bottom of the lens barrel. Therefore there is no "unbalanced" combo (when considering normal weight lenses <1.5 - 2 kg).