RF800 vs EF400+2x

Hi all,
I have been looking for some more reach out of a telephoto for some time, but have held off as until I went mirrorless (R6 with IBIS)

I recently just missed out on a really good deal on a EF400 f/5.6L which got me thinking.

I currently have an EF70-200 f/2.8L and 2x (Mk3).

I can still easily get an EF400 f/5.6L secondhand for less than the new RF800 f/11. Given that I already have a 2x, that would give me up to 800mm at f/11 with the combo, the same as the RF800 but without lens IS, it also gives me the option of 400mm at f/5.6 (something I can already get with my 70-200 + 2x). I have IBIS in my camera body which would help with the lack of IS in the combo.

Thoughts? The other entirely different option is to ditch my nearly 15 year old 24-105 /f4L and replace with the RF version, but that is another story...

Are you happy with the 70-200mm plus 2x results? Like good enough that you don't pine for a 100-400mm MkII?

If so than it might be worth considering.

It's an interesting idea, as with the the new R bodies AF should be just fine. I assume you'd have to stop down past f/11 for best results, or to get close to the 800mm bare lens sharpness,. but many seem to like the 2X on the zoom, so the prime could be better.

I'd love to hear from someone that has tried the 2X on the old rocket on an R5/6!

The old budget won't survive the Mk2 100-400, although I have considered it a lot given how often I have the TC on my 70-200.

Now I have gone the R way though I have spotted the 100-500, however it is way beyond my budget right now.

Actually I think I have changed my mind again, I sold my 6D plus extras last night and that got me nearly half way to a 100-400 Mk2...

FlyingPete wrote in post #19186997
...I have been looking for some more reach out of a telephoto ... I recently just missed out on a really good deal on a EF400 f/5.6L which got me thinking....I can still easily get an EF400 f/5.6L secondhand for less than the new RF800 f/11. ...

(Keeping with the cost used lenses)
I'd bet the image quality of the 400mm prime + the 2X ext will beat out the 100-400 + 2X ext.
If you think you'll end up using it at 400mm most of the time anyway rather than 600mm (300mm x2) that is another vote for the prime over the zoom.
For me, at 800mm, I would need the lens to be supported by something/anything so I wouldn't be concerned about stabilization as a top deciding factor.
Just my thoughts.

In short, 'it depends'. Keep in mind the fundamental fact that any teleconvertor magnifies the inherent optical weaknesses of the lens, along with magnifying its FL.

Some lenses do not fare well with teleconvertor on them; others are less prone to greatly magnified shortcomings. The 70-200 from Canon has traditionally done quite well in testing with teleconvertor, with scarely noticeable degredation that quantified to about -10%. The 100-400 v1 was especially 'not good' with teleconvertor.

I ended up thoroughly blowing my budget and splashed for a 100-400 Mk2, I had that bad boy out and about this morning and I think it will be far more useful than either of the two primes, the question in my mind is will I keep the 70-200? Time will tell...

FlyingPete wrote in post #19188501
I ended up thoroughly blowing my budget and splashed for a 100-400 Mk2, I had that bad boy out and about this morning and I think it will be far more useful than either of the two primes, ...

It's an extremely popular lens because it's an extremely good lens, and it plays very well with the 3rd gen extenders. I had mine on the camera just yesterday while the puppy played in the yard. No matter where she wandered I was able to frame her as I wanted.

FlyingPete wrote in post #19188501
I ended up thoroughly blowing my budget and splashed for a 100-400 Mk2, I had that bad boy out and about this morning and I think it will be far more useful than either of the two primes, ..

It's quite an amazing zoom!

CyberDyneSystems wrote in post #19188966
It's quite an amazing zoom!

Have you used a sigma extender and the canon 2x iii?

Which one would be better to pair with a 150-600mm?