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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.



Good, and at this point, Feb 2023, if I buy any sigma lense, will it work fine (autofocus) on my R5C?



No guarantee there.  In photo mode AF may work, video mode is a different story.  I'd stick with Canon glass to ensure function on both sides.  

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, 430EX III-RT ~DxO PhotoLab Elite ~DaVinci Resolve ~Windows11 Pro ~ImageClass MF644Cdw/MF656Cdw ~Pixel 8
~CarePaks Are Worth It

It doesn't seem to be limited to 3rd party lenses, I've heard of others having issues with certain Canon EF L series lenses as well, such as the 85mm 1.2 L and the 16-35mm/17-35mm etc...

I hope that someone at Canon is aware of how disappointing it is for us loyale users to learn that our older investments are turning into thousands of dollars of paper weights if they choose not to include lens support for legacy EF glass. It's such an insult to users who have been buying Canon forever. 

I hope they fix this in the next firmware update and just implement compatibility for ALL ef glass, regardless of the makers, Sigma, Tamron, Canon or otherwise.