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R5 C won't work with Sigma lens in video mode, but works in photo mode


Quick question to see if anyone knows what the problem could be

Canon R5 C camera with the EF->RF adapter (the one with the control ring) plus a Sigma EX series 10-20mm lens. This is a crop sensor lens.

when I use this combination together in video mode the camera says the lens is not compatible. the aperture value cannot be read and cannot be changed, Autofocus will not work etc. However without changing anything in hardware if I switch the camera into photo mode it works just fine. Anyone know what could be going on?

One other note even in photo mode the camera did not recognize this lens as an APS-C format lens so I had to change the setting manually. other Sigma lenses which are APS-C format are recognized as such automatically and the camera is put into crop sensor mode. I don't know if that means anything but could indicate a minor incompatibility which I hope could be corrected in the future.



Given that the lens is third-party, and isn't recognised as crop, I would guess it's not fully compliant with the EF communication protocol standard.  Which isn't too surprising, as there really isn't a standard; it's a mish-mash which has changed over the years.

Since the R5C really has two different operating systems, it's not a huge surprise that the two sides treat an alien lens differently.

I wouldn't be surprised if this lens works generally with Canon stills cameras, but has issues with their cine cameras.  If true, that would mean that Sigma haven't done the full job of making this lens compatible -- again, since they're reverse-engineering the protocol from scratch, not a huge surprise.

See if Sigma have a firmware update for that lens.


Have you turned on Lens EF-S mode in the video menu? I assume it's there. On the C70 it's in the first tab (Camera Setup) at the bottom of Page 6.

But yes, AtticusLake is certainly correct above that ultimately, it's a Sigma lens issue. Do you have the Sigma USB dock? There may be a firmware update for your lens.

I have tried  EF-S mode, same effect unfortunately.

Sigma docks only work on Global Vision lenses.  Art, Sport and Contemporary.  

This EX series lens is about 8 yrs.  There are 2 variants and are not included.

Both also have the following limitation.  * Vignetting will occur if the lens is used with digital cameras with image sensors larger than APS-C size or 35mm SLR cameras.  Fair to say its lucky it works in Photo mode.

Bay Area - CA

~R5 C ( ~RF Trinity, ~RF 100 Macro, ~RF 100~400, ~RF 100~500, +RF 1.4x TC, +Canon Control Ring, BG-R10

~DxO PhotoLab Elite ~DaVinci Resolve ~Windows11 Pro ~ImageClass MF644Cdw ~Pixel 8 ~CarePaks Are Worth It

yes, I bought it new 2-3 years ago but its been discontinued. Unfortunate, its a pretty good lens I wish I could use it on this camera. It just puzzles me that in photo mode it works but in video mode it does not. I guess it really is like two completely separate cameras hybridized into a single body. Pretty remarkable actually. I think the solution is going to be investing in an ultrawide RF lens and keep the Sigma on my DSLRs

Good Idea.  I've owned 3 Sigma lenses,  all have been stellar on DSLR.   

Bay Area - CA

~R5 C ( ~RF Trinity, ~RF 100 Macro, ~RF 100~400, ~RF 100~500, +RF 1.4x TC, +Canon Control Ring, BG-R10

~DxO PhotoLab Elite ~DaVinci Resolve ~Windows11 Pro ~ImageClass MF644Cdw ~Pixel 8 ~CarePaks Are Worth It


I'm having a similar problem but with a Sigma 35mm Art 1.4. The R5C in video mode also says the lens is not compatible and nothing works. On photo mode, no problems at all. I bought this lens at 2014 and I never had the chance to update it on a dock. But what's intriguing, is the fact that the Sigma 50mm Art 1.4, bought at the same time as the 35mm, works normally! And also other intriguing fact, I have a R5 too, and everything works perfectly! No incompatibilities whatsoever. I really don't think the problems are on the lenses. Already updated the camera to latest firmware, still not working.


Actually, it is the lens and its ability to correctly communicate with CineOS.  I'm sure it would probably exhibit the same behavior if you mounted it on a C70 or other Cine Mode camera.   Video mode on the standard R5 and others is a different animal.

It looks like the 35mm got support for CineOS in FW version  1.03




Autofocus is supported at any aperture value when used with the Canon Digital Cinema Camera EOS C100.

Last update was Nov of 2020 v2.0.2

Firmware download | Support | 35mm F1.4 DG HSM | Art | Lenses | SIGMA Corporation (

If you live in the bay area, I'm happy to flash it for you with my dock.  

Other possibilities. 

See if you can view EXIF data for the camera and lens in DPP.  The Sigma lens is not supported, but you may get some additional info about your lens.

I believe DxO (my editor of choice) which does support 3rd party lenses captures the Camera's as well as the lenses FW values, if I recall.  I'm just trying to figure out a way for you to verify which FW your lens has to see if its worth flashing.  The 35mm EF is one of Sigma's best Art lenses and would be great for video if you can get it to work.  Of course, I recommend that you use a Canon branded EF to RF adapter/control ring for the best possible outcome. 

Bay Area - CA

~R5 C ( ~RF Trinity, ~RF 100 Macro, ~RF 100~400, ~RF 100~500, +RF 1.4x TC, +Canon Control Ring, BG-R10

~DxO PhotoLab Elite ~DaVinci Resolve ~Windows11 Pro ~ImageClass MF644Cdw ~Pixel 8 ~CarePaks Are Worth It

Good point about the Cinema OS.  I also doubt if all of the features of Movie Servo AF work with many third party lenses.

"The right mouse button is your friend."