DavidM Loc: New Orleans, LA

Some good info regarding that lens here - https://www.kenrockwell.com/canon/eos-r/lenses/800mm.htm

dikh123

I have shot with the Canon 1Dx MkIII and the Canon 600mm f4 and recently purchased the Canon R6 and 8oomm RF f11. The lens came while I was at work, so I did not get out until near dark that evening. The lens is crisp, the camera handles high ISO amazingly! I was floored when I reviewed the images at home. DOF was reasonable, and where I saw only silhouettes, the camera captured color abound! I attribute that partially to the lens being so well engineered. Can't wait until the weekend when I can run this combo through its paces.

joer Loc: Colorado/Illinois

On a ILC focusing takes place at wide open regardless of the aperture setting and then stops down at the moment of exposure.

On fixed aperture lens focusing takes place at the only aperture available. At f8 & f11 you are relegated to very bright high contrast scenes. Shooting early morning or late evening is nearly impossible. Forget low light situations altogether.

I had experience with a used Nikon 500 f8 reflex lens. After experimenting with it for a time I donated it to a sibling and took the loss. I think he didn't use it for very long too.

If this doesn't concern you then it may be a good purchase for you.

petrochemist Loc: UK

That is usually the case, but not with all interchangeable lens cameras, or all lenses.
None of my large format cameras/lenses have any link between shutter & aperture, stopping down is totally manual even when the shutter release is only a few millimetres from the aperture control.
Early M42 SLRs didn't have this option, and the later ones wouldn't with the earlier lenses. I'm sure there are plenty of other examples of ILCs before auto stop down was introduced.
Adapted lenses don't usually have any auto stop down capabilities irrespective of the lenses native capabilities.

Mustang1

Being that the lens is fixed at f11 and you are accustomed to shooting at f8, you will have greater depth-of-field. You may need to increase the ISO since you are shooting at a smaller aperture. A tripod definitely will reduce blurr. Best Wishes!

Bill_de Loc: US

I just looked at and compared a number of Regis's images. I think he got his sharpest pictures with better contrast when he was shooting with his Canon 5Dsr - Canon 300 2.8 II - Canon 2x III.

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imagemeister Loc: mid east Florida

- I like the 400 DO II with 2X III also .....

amfoto1 Loc: San Jose, Calif. USA

You should do an online search for the many reviews of the new Canon 600mm and 800mm RF lenses. There is lots of user feedback. I've watched videos about these lenses from Jared Polin (FroKnowsPhoto), Tony & Chelsea Northrup, Gordon Laing, FStoppers, dpreview, and Christopher Frost. There are many others who have posted videos or written reviews about these lenses. Some (such as Jared Polin) initially were really dismissive of the lenses... until they actually tried them. There's at least one interview with a Canon executive who said we might expect to see more of these types of lenses in the future, so they must be seeing good sales and positive user feedback.

Yes, they're limited in some ways. But so long as your subject isn't too close to the background, you can still get a lot of blur to make the subject stand out. Also, the lenses are not weather sealed and largely plastic to keep them light weight. But they appear to be capable of making excellent images and the alternative is 10X the price or more. There is expected to be an RF 600mm f/4L in 2021... but you can bet it will cost well over $12,000. The current EF 600mm f/4L III is priced that way. So is the EF 800mm f/5.6L. Those EF 600mm and 800mm also are pretty big, hefty beasts, although Canon has done a lot to reduce their weight and there may be some things they can do with the RF version to further shave size and weight. But you can only do so much with a big, hefty lens!

https://www.bhphotovideo.com/c/compare/Canon_RF_600mm_f_11_IS_STM_Lens_vs_Canon_EF_600mm_f_4L_IS_III_USM_Lens_vs_Canon_RF_800mm_f_11_IS_STM_Lens_vs_Canon_EF_800mm_f_5.6L_IS_USM_Lens/BHitems/1573780-REG_1433722-REG_1573779-REG_542293-REG

Personally, if I were to switch to one of the R-series cameras, I'd plan to get the RF 100-500mm zoom and probably pair it up with the RF 800mm f/11. Maybe initially I'd just use an EF to RF adapter and the EF 100-400mm II lens and EF 1.4X teleconverter I've already got.

I've used the Canon EF 300mm f/2.8 and 500mm f/4 for many years and it's simply not practical to try to carry them both at the same time. One is approx. 6 lb and the other about 8 lb. The same can be said for all the EF "super telephotos". No matter how great those lenses are, few people would take more than one of them out to shoot at a time, which itself is pretty limiting with these big primes.

But since the RF 800mm f/11 only weighs around 2.75 lb., and the RF 100-500mm is right at 3 lb., that's a very manageable combo (even with one or two shorter/wider lenses and a body or two with grips).

joer Loc: Colorado/Illinois

Those are not ideal camera/lens for wildlife or fast moving subjects. Sure the ops prospective lenses can get a decent photo if the light is right otherwise you are on a tripod and manually focusing.

In the distant past I had a manual 500mm f4 lens which was used for bird photography. The images were great when I nailed the shot which was not that often compared to my kit today.

If you liked to be challenged those f8/f11 aperture lenses will really appeal.

ecurb Loc: Metro Chicago Area

A Canon lens with a fixed f11 is a far cry from a back of the magazine Spiratone T-mount special. Canon made an affordable long lens with great potential image quality for eight thousand dollars less then the cost of a f5.6 lens. Remember your image quality depends more on the ape behind the camera then on the lens.
🙈

CHG_CANON Loc: the Windy City

With the wrong camera, success is probably 99% luck. But with a mirrorless camera, it's 100% the photographer.

tjkraemer1 Loc: Maryland

That is so true. I wonder how many critics actually had the R5/F11 combo in their hands before they made such claims.

Dickbas Loc: Southern New Jersey

Hey Dave, check this out the Focus on this shot of a PinTail. Canon R5 with RF800mm F11.0, at only 1/250 sec !!!, ISO 160, HAND Held by a very Shaky 73 Yr Old!!!!!

Or, this one of a Snow Goose flying overhead in really Overcast skies. 1/6000 sec, F11.0, ISO 2500, Hand Held!!!

Got my R5 and 800mm last Thursday and this was taken on Friday or Sun at Forsythe NWR.
I couldn't be more pleased with my purchase. Merry Christmas to Me!
Will be selling my $11,000 200-400mm F4.0 with built-in 1.4x Conv, my $6,000 1Dx, and my $2,500 EOS 5D Mk4!
Any buyers out there???

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Jimmy T Loc: Virginia

With you, there is no time to duck.
I really look forward to being slapped in the face with reality, and facts!!!
Thanks for always for being there to clarify these spurious and random UHH observations.
I know that you can't (and don't) make this stuff up. . .
Smile,
JimmyT Sends

TRSquared Loc: South Carolina

I know this is an old post so this idea probably will not help Roe Cole on his problem but here is what I do when faced with this kind of decision. I rent the lens for a week or two when I have plenty of time to give it lots of work in the field. I just checked the Canon RF 800mm lens at lensrentals.com and it rents for $46/week. They will often apply your rental payment to the purchase if you chose to keep the lens, but you are buying a used lens even if lightly so and KEH or others may be a better financial option for purchase.