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Latest C70 firmware ( created a problem with IRIS control of Tamron lens


Since I updated the C70, i can no longer change the iris on my Tamron 24-70 lens.
Did some troubleshooting: I used the lens with another camera = works fine.
Used another lens (Canon 70-200) on the C70 = works fine.

How can i downgrade the firmware? I cannot find any older version to download.
Is there a way for canon to check this problem?

Thank you


Product Expert
Product Expert

Hello Kokorniokos,

There is not a way to back track the firmware unfortunately. Canon does not support or have the capability to troubleshoot third-party items. I do apologize for any inconvenience this may have caused.


I just bought the Tamron tap-in console for 80euros, and updated the lens firmware to v2. Unfortunately the problem persists. The inconvenience  is the fact that I now have to pay over 2000 euros for a new 24-70 lens, ofcourse by Canon to ensure compatibility. Isn't there any solution, or help on the matter? The people that are developing the firmware, can't be notified of the issue and resolve it in the next release? Isn't Canon able to  -at least- offer a discount coupon for purchasing this super expensive lens, that i am now forced to buy? 



Respectfully, its not Canon's responsibility to ensure their cameras work with 3rd party products.  This is up to  Tamron, Sigma and others.  Its possible that the feature or improvements introduced with v1.0.8.1 are not supported by the Tamron lens.  Cinema products are more finnicky than still cameras.  

I had the Sigma f2.8 version of your lens that I used for years on my 6D2.  I adapted it to my R5 C and was able to continue using it, but I noticed it performed more slowly in video mode.  Focus, etc was still sharp, but acquisition and tracking was slower, etc than what I was accustomed to.  This prompted my migration to RF glass.

Now that Canon, Sigma and Tamron have reached licensing agreements, we are going to see new RF glass coming from both lens makers. However, this doesn't mean older lenses will become compatible with 100% functionality.

My advice is buy the Canon RF 24-70 and sell your Tamron.  Iris control will work automatically or manually without any problem.  

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


Thank you both for the replies, I appreciate your time.