RF to M Adapter?

SDFilmFan · Dec 6, 2018

Ok, I have an adapter to use my EF and EF-S lenses on my M and M50. If I bought an R I could also get an adapter to use the same lenses. The question is whether there will be an adapter to use these wonderful RF-mount lenses on M body cameras? Is it possible geometrically?

I have already decided I probably won't be buying any more EF lenses as the future looks RF and M. The eventual replacements for my 5D3 and SL1 will likely be mirrorless. But will there be a divide between the two mirrorless lines?

Mike E

Mt Spokane Photography · Dec 6, 2018

Very unlikely, the lens would have to sit inside a M or the adapter have some complex optics. EF lenses are the universal solution. The issue is due to the 18mm the rear of a RF lens sits from the sensor, while the M is designed for lenses to be 20mm from the sensor. Any adapter using lenses to make it work will likely be a kluge or very expensive.

tapanit · Dec 7, 2018

SDFilmFan said:
Ok, I have an adapter to use my EF and EF-S lenses on my M and M50. If I bought an R I could also get an adapter to use the same lenses. The question is whether there will be an adapter to use these wonderful RF-mount lenses on M body cameras? Is it possible geometrically?

I don't think it could be done without optical elements and that'd mean it'd be expensive or lose too much image quality to make sense. Also it isn't clear how easy it would be to do electronically - do RF lenses work without all the extra pins M bodies have no idea how to use? If not, the adapter would also require complex electronics, driving the price even higher. So I doubt one will ever be made.

One caveat though: a speedbooster-type adapter could make sense. It would still be expensive but the price might be more palatable if you get bigger apparent aperture as extra benefit.

padam · Dec 7, 2018

Mt Spokane Photography said:
Very unlikely, the lens would have to sit inside a M or the adapter have some complex optics. EF lenses are the universal solution. The issue is due to the 18mm the rear of a RF lens sits from the sensor, while the M is designed for lenses to be 20mm from the sensor. Any adapter using lenses to make it work will likely be a kluge or very expensive.

It is exactly the opposite: 20mm for RF and 18mm for EF-M

The question has been asked in an interview before and the answer from Canon's representative was: "It can be done, but at the given size, the tolerances have to be extremely tight to do it". So I think what he meant was: it is not feasible.

tapanit said:
One caveat though: a speedbooster-type adapter could make sense. It would still be expensive but the price might be more palatable if you get bigger apparent aperture as extra benefit.

A focal reducer already exits.
It works for FF EF lenses (or APS-C as well if one is intending to shoot cropped 4k on the M50)

Canon might make an own version (the patent suggests it would be 0.8x instead of 0.71x) that will cost more.

jolyonralph · Dec 7, 2018

I think it highly likely that if Canon are doing an EF->EF-M speedbooster they will also do an RF->EF-M speedbooster.

andrei1989 · Dec 7, 2018

Mt Spokane Photography said:
Very unlikely, the lens would have to sit inside a M or the adapter have some complex optics. EF lenses are the universal solution. The issue is due to the 18mm the rear of a RF lens sits from the sensor, while the M is designed for lenses to be 20mm from the sensor. Any adapter using lenses to make it work will likely be a kluge or very expensive.

it's the other way around: R has a flange distance of 20mm and M has 18mm so in theory you could have a 2mm adapter but it's tricky to fit any electronics inside..

padam · Dec 7, 2018

jolyonralph said:
I think it highly likely that if Canon are doing an EF->EF-M speedbooster they will also do an RF->EF-M speedbooster.

The latter is not possible, you can only use SLR lenses covering a wider sensor area with a speedbooster, there is a simple explanation here:

jolyonralph · Dec 8, 2018

padam said:
The latter is not possible, you can only use SLR lenses covering a wider sensor area with a speedbooster, there is a simple explanation here:

It's perfectly possible. RF lenses cover the full frame area, so with a speedbooster an RF lens could theoretically be adapted to compress the output down to an APS-C coverage of the EOS-M sensor. As it has optic elements to adjust light path you can work around the fact that the RF lens and EF-M mount have very similar flange distances although I'm sure it's not as straight forward as an EF->EF-M speedbooster it's absolutely possible.

Rocky · Dec 8, 2018

jolyonralph said:
It's perfectly possible. RF lenses cover the full frame area, so with a speedbooster an RF lens could theoretically be adapted to compress the output down to an APS-C coverage of the EOS-M sensor. As it has optic elements to adjust light path you can work around the fact that the RF lens and EF-M mount have very similar flange distances although I'm sure it's not as straight forward as an EF->EF-M speedbooster it's absolutely possible.

All of these in 2 mm space??? Good luck to that

Mt Spokane Photography · Dec 8, 2018

andrei1989 said:
it's the other way around: R has a flange distance of 20mm and M has 18mm so in theory you could have a 2mm adapter but it's tricky to fit any electronics inside..

When you get old like me, your memory is not always reliable, I should have checked.

jolyonralph · Dec 9, 2018

Rocky said:
All of these in 2 mm space??? Good luck to that

You can make a speedbooster wider than the flange distance difference because the optics can adjust for the difference in flange distance.

Canfan · Dec 19, 2020

Would be nice to use an RF 100-500mm lens on my M6 mkii though

Linteria · Dec 23, 2020

jolyonralph said:
I think it highly likely that if Canon are doing an EF->EF-M speedbooster they will also do an RF->EF-M speedbooster.

The problem is, to my knowledge, there is no such EF-EFM speedbooster from Canon on the market or in the works. Only 3rd party. But i would love an RF-EFM adapter, even without focal reducing optics. I'm less than 4 months into my first M mount cameras. Future-proofing them would be amazing.

Eagle Eye · Dec 28, 2020

I think a speed booster from Canon would make a lot of sense. It future proof’s your purchase of Canon products. I abandoned my 6D and EF L glass to build an M system. I’d love to add some RFs to it. When Canon eventually drops the M system, my possession of RF glass would make switch to the R system far more likely than going to another brand. I think Canon would be foolish to abandon the M system before they’ve found a way to encourage M shooters to purchase RF glass (or an EOS R body to use with EF-M glass).

jolyonralph · Jan 2, 2021

Linteria said:
The problem is, to my knowledge, there is no such EF-EFM speedbooster from Canon on the market or in the works. Only 3rd party. But i would love an RF-EFM adapter, even without focal reducing optics. I'm less than 4 months into my first M mount cameras. Future-proofing them would be amazing.

Well, two years on that never happened, and Canon aren't doing an EF anything any more. I also doubt they'll do speedboosters.

You'll never get any adaptor to do RF to EF-M. It can't happen. EF->EF-M speedboosters already exist though.

jolyonralph · Jan 2, 2021

Eagle Eye said:
I think a speed booster from Canon would make a lot of sense. It future proof’s your purchase of Canon products. I abandoned my 6D and EF L glass to build an M system. I’d love to add some RFs to it. When Canon eventually drops the M system, my possession of RF glass would make switch to the R system far more likely than going to another brand. I think Canon would be foolish to abandon the M system before they’ve found a way to encourage M shooters to purchase RF glass (or an EOS R body to use with EF-M glass).

The M bodies can't understand the RF protocols, which are done with a more modern faster interface than either EF or EF-M. So, no way that RF lenses will ever be adapted to EF-M bodies, sorry.

mangobutter · Jan 21, 2021

You'd likely lose inifinity focus even if you could create a 2, 3, 4, 5+mm adapter.

You could always just free lense it for fun. I've done all sorts of frankenstein freelensing. I "mounted" my Fuji glass up to the Canon RF flange. Some of Fuji's lenses project so large, that it covers the entire full frame area. However Fujifilm lenses are focus by wire so I have to mount to my Fuji body first, tune the focus distance that i desire, dismount, and free lense onto Canon R. It's messy but it works. I could post up some pics some time soon. You can try this with any mirrorless lens. Obviously its just for fun and experimentation and not practical for real photography. but if you wanted to, you could. Conversely I've tried Canon RF glass on Fujifilm bodies.

I'll try my Fujifilm 56mm 1.2/R on Canon R and see what happens =p

phile · Feb 7, 2021

Eagle Eye said:
I abandoned my 6D and EF L glass to build an M system.

Why would you not use EF L glass? My EF 100-400 L Mark 2 gives stunning results on my M6 Mark 2.

SteveC · Feb 7, 2021

phile said:
Why would you not use EF L glass? My EF 100-400 L Mark 2 gives stunning results on my M6 Mark 2.

I can attest to this.

Yes, the lens looks absurdly huge on that little body, but you're not taking pictures of your camera.

phile · Feb 7, 2021

SteveC said:
I can attest to this.

Yes, the lens looks absurdly huge on that little body, but you're not taking pictures of your camera.

No, I'm not.

18 IMG_7882 by philethier, on Flickr

Canon EOS M6 Mark II
EF 100-400mm f/4.5-5.6L IS II USM
ƒ/5.6 400mm 1/1600 400iso

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