starlifter Loc: Towson, MD

I use a Sigma !50-600C on my D850, no complaints. I may trade it in eventually on a Tamron 150-600 G2 as I already have 4 other Tammys and all work very well.

DaveJ Loc: NE Missouri

I have the R5 also. I am using a EF 100-400 II. I have had good results with a 1.4 version III. I also own the RF 800 F11. It has served me well for close to a year. They also have a 600 F11 for $200 less($700). The RF 100-500mm is a high quality lens and from results of others work very well with the RF 1.4 convertor. It is hard to find and is pricey($2799), which has kept me from getting it since I own a good 100-400 II. Some reviewers have said it is not as well built as the 100-400 using more plastics, but time will tell and I have not heard complaints from owners, just reviewers. Good Luck.

Bill_de Loc: US

I used it on a D4s, D500 and D850. I guess they all have poor low light focusing capability. What camera would you recommend?

I think it more likely, as I said, that I got a bad copy of the lens. My longest lens has a maximum aperture of F/5.6 and focuses fine on the cameras mentioned.

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Ruthlessrider

Thank you all for you comments and suggestions. This is the prime reason I belong to this group. Thanks again!

Canisdirus

Canons RF lens inventory is still incomplete.
But, I would suggest for now the 100-400mm RF lens...or the 300mm f/4 RF prime.
You can go with the 800mm f/11 RF...but the image background will be....less desirable.

Thomas902 Loc: Washington DC

"... I’m looking for suggestions for a lens that will perhaps go out to 600mm that has near the quality of the canon 70-200mm..."

I had to smile... Shooting a 600mm for wildlife may be a bit of a challenge.
It's not so much the glass here in as much as the skill and technique of deploying a long lens.

Would advise you to rent first... And see how comfortable you are at actually shoot at 12x

I let a colleague try shooting my 200-400mm at 400mm on a crop body...
Their first question? How do you follow the soccer ball?
Yep, it's the photographer not the glass at 12x...

Just saying...

And yes Canon makes some of the very best super telephoto primes available on the market.
All the best on your photographic journey Ruthlessrider

Ruthlessrider

Here’s a question I think of every time I go into a photo shop that sells multiple brands, invariably the store clerk tries to convince me that there are only two factories that produce these lenses, so Canon is not better than Nikon, which is not better than Tamron, which is not better than sigma, etc., etc. Is it really just all about quality control specs demanded by the company whose name goes on the lens?

Canisdirus

No, it's also the design that makes the differences, not just quality control.
The devil is always in the details.

imagemeister Loc: mid east Florida

Another GOOD option for you is the Canon 400mm f5.6 L and the Canon 1.4X and 2X that will AF on the R5. Canon lenses are your BEST option.
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davidrb Loc: Half way there on the 45th Parallel

You may regret selling your 70-200mm f/4.0. It is a very versitile lens that has very distinct applications. Might be the best $500.00 lens on the market today. Very light-weight and semi-long, it is capable of producing great images. And........it is already paid for!

CHG_CANON Loc: the Windy City

The IBIS-enabled mirrorless cameras are breathing life into older lenses, lenses that are exceedingly sharp, maybe with larger sizes and weights than the more modern releases.

Look at the used options for

EF 300 f/4L IS - use your 2x to an effective 600mm
EF 400 f/2.8L - let the camera add the IS to this model that ranks as one of Canon's sharpest ever, double to effective 800mm
EF 300 f/2.8L - let the camera add the IS to this model that ranks as one of Canon's sharpest ever, double to effective 600mm
EF 500 f/4.5L - let the camera add the IS, double to effective 1000mm

Many of the list above also include newer IS-enabled vI / vII models. The risk of going very far into the past is the potential for the need of a future repair, where parts don't exist and the lens would just become a brick / doorstop. But, the lenses were build for professional everyday use in all-weather conditions. They're built to last forever.

Personally, I've been going even further back into the past, back to the 1980s vs the 1990s of the EF models. Here's some success with a 500L manual focus lens: https://www.uglyhedgehog.com/t-712890-1.html , many of these images with an FD 1.4x extender to an effective 700mm mounted to a 24MP Sony mirrorless.

suntouched Loc: Sierra Vista AZ

Canon is releasing a new RF 100-400 mm lens which is reasonable in price, size and function. It's available for pre order.

CHG_CANON Loc: the Windy City

It's going to be an f/5.6 to f/8 zoom at a reasonable price, leveraging the focusing and higher ISO abilities of industry leading EOS R technology. There's a lot of options both in the new RF offerings and the legacy lenses.

MrPhotog

Unless you desperately need the cash to finance that new lens, I’d suggest you keep the 70-200 that you are happy with. Add to it, rather than replace it. You’ll find plenty of other uses for it.

Consider some old, used, long lenses. Look at ebay. In addition to Canon lenses You can get Novoflex 600 mm and Leica 560 mm lenses for well under $1000. A fraction of what they sold for new. Great optical quality, and there are adapters so they fit your camera. But forget autofocus or automatic apertures. Thinking of adapters, you may be able to find one to use Nikkor lenses on your Canon.

stillkickin Loc: Coastal Bend of Texas

I agree. I rented on and ended up keeping it an extra wk. Now to make the purchase.