Hallo,
so far Canon does not offer extension tubes for the RF mount. But various third party providers do.
I seek both pos. or neg. experience with those third party tubes. Anybody can share something?
Quality, problems, just works, …
I am not seeking general infos about extension tubes.
since extension tubes have no optical component a third party product should be fine. I bought an EF to RF mount adapter from a third party for a third of the cost of Canon’s and it is excellent. It is a metal extender with electrical contacts.
I assume there might be quality differences between the manufactures, even so it is a simple tube with contacts. Therefore I did ask for experiences.
Read the reviews and look for tight/loose fit, if they are manufactured to the right tolerances you will be OK. Problems are usually mechanical.
FWIW, I found Meike reliable, but I used it on other mounts, not RF. Reviews for RF specifically seem OK too. If you get problems, they are usually apparent from day 1 so you can just return them.
Do you have to have electrical contacts? If fully manual is OK, your life will be much easier 
Ref: https://discuss.pixls.us/t/fun-with-lenses
Have fun!
Claes in Lund, Sweden
I bought mine from Amazon and their returns policy meant if I was unhappy with the mount I could return it. So that made it a safe purchase for me. It is a nice fit on my camera and the brand was Andoer EF-EOS R adaptor.
How so? Electrical contacts give you lens metadata (FWIW) and aperture control (when the lens has no ring you need it), and also MF if it is by wire. But they don’t take away anything.
As far as I know, all RF mount lenses have electronic aperture and are focus by wire, so a tube without contacts would make the lens absolutely unusuable … unless OP plans to use an old lens. Most lenses are like that for a long time by now, even late DSLR lenses were usually like that.
Contacts are wished, but MF and old lenses are in the picture as well.
Really nice shots btw.
my adapter has electrical contacts and that means stabilisation, focus and aperture control are all available. Slightly off topic but I also use some totally manual lenses with no electronic contacts and they work fine once I go into the menu and tell the camera to fire without a lens attached. I mention this because tubes without contacts may still work if you can set the aperture on the lens itself.
Regarding stabilization and focus: although the camera reports them as being available, are you sure that they work as expected?
I am asking because, given how those extension rings work, the camera is effectively being lied to about the focal length, and thus all calculations it performs are off.
This is a good point that I am very prone to forgetting. On my EM5ii with a manual lens, one can enter focal length manually (as most bodies AFAIK) but the active ‘image de-stabilization’ when a drastically wrong focal length is entered is hilarious and/or terrifying depending how long it takes me to remember what I did 
I can only say the stabilisation and focus were highly effective. Since it is an adaptor the focal length is not changed. It is just giving the correct spacing for the mirrorless camera body.
Well, yes, that’s true, of course, for an adapter (or it would be pretty useless).
But the question was about extension rings, where the lens is moved away from the body for closer focus. That does change the calculations needed for image stabilisation (though working with extension tubes without a tripod is not for the faint-hearted, and with a tripod, IS isn’t needed).
I may be wrong but I doubt an extension ring would screw up the lens’s or the cameras image stabilisation function. But I may be wrong. I doubt a genuine brand exentsion ring would be any different to a 3rd party extension tube. Maybe someone else can share their experience. I am 100% pleased with my adaptor which is made by Andeer. Just sharing my experience.
You are right in the mathematical sense: the focal length applies when the lens is focused at infinity, and that is unchanged.
However, when doing macro, you are interested in the other edge of the distance range. Generally, modern IBIS takes the focus point distance and location into account when it has access to that information. When you manually specify the focal length for a lens without electronic contacts, it cannot do that and works in a reduced mode.
Extension tubes with pass-through contacts are an interesting interim case: the camera may imagine that it has access to all kinds of information about the focal point (for AF lenses), but all that information is wrong. In particular, yaw/pitch corrections may be grossly incorrect, that subject is much, much closer now.
Practically, I would agree with @rvietor though: handheld macro becomes very difficult at large magnifications, so you are using a tripod anyway and IBIS will be suppressed automatically.
For handheld macro, I would just do test shots with and without IBIS.
I am not shure if the IBIS is automatically supressed when using a tripod. With my Canon R6 this has to be configured manually in my understanding.
Nonetheless. Should be deactivated when using a tripod,
Some time ago I have watched a video where a guy tested what’s the slowest shutter speed he can use for handheld macro with lens VR, IBIS and without. I think the result was that for super close ups stabilization didn’t have a noticeable effect.
sounds sensible advice.
Once you start approaching 1:1 you need to get a flash or you’ll run out of enough light due to inverse square law bellows factor, and with a flash you don’t need to worry about stabilization at all if you expose correctly. You’ll have to stay still anyhow to be able to focus 