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Aperture flicker on C70 with older Sigma 50mm f/1.4 and .71 EF to RF adapter


Hi there,

I have the Canon C70 (latest firmware) with the Canon .71X RF to EF adapter and a Sigma DG HSM 50mm f/1.4 lens (not the newer Art version). Every once in a while the aperture will start to flicker and there is no way to make it stop except to turn of the camera. I don't know what is causing it. Lens and camera compatibility? Lens and camera plus adapter compatibility? Lens failing? Something else? To be clear, it is a manual flickering that I can see on the screen and hear happening, not the kind of flickering that comes from setting the wrong shutter speed under certain lighting conditions.

Any thoughts are very much appreciated. Thanks in advance.




I have a canon EOS C70, it's intermittently having these issues. Another acquaintance is having the same problem, and I found your issue online too. Looks like you are not alone!

Basically what happens is you'll notice the screen begins to flicker/flash, (when not recording) and it almost looks like the shutter speed is wrong and picking up artificial lighting poorly, (but that isn't the issue) and if you go to try and alter a setting or record, the camera won't respond, so you are forced to turn it off. When you try to turn the camera back on, it wont restart, almost like it's a computer crashing. We have found the only temporary fix is to remove the battery and replace it. So far, for both of us this has allowed us to continue filming as we were, hope this helps you too. 

We havent noticed that it's audible to the user, but we haven't been in quiet environments and naturally when the issue occurs during filming we are panicking and trying to get it to stop quickly so we can continue filming so are not concentrating on this I guess. Interestingly, we both have the 50mm sigma f1.4 Art lens and have been using these, I am not sure if it's always happened with this lens attached but I will try to make notes of the exact circumstances in which it happens to look for patterns. 

It's happened to both cameras (mine and the other persons) several times, it happened twice in one day to me on Saturday. It's interesting though because the cameras are very similar in age but their camera has the new firmware and mine isn't updated and their camera has seen much more use than mine. But the issue began happening within the same few weeks for both of us. 

Have you had this issue for long, how often is it recurring etc?

PS. I contacted Canon CPS today on +44 (0) 800 9150009 and spoke to a guy called Gavin who said he would be investigating it. Have you contacted them, if not, then it would be a good idea so you can get his feedback too.


Thank you, mollybrown789. That all sounds very similar to my issue. Curiously, I have since upgraded to the Sigma 50mm f/1.4 ART and I haven't had the same issue. There was one time that the flickering effect appeared in my footage withing Adobe Premiere Pro but not while I was shooting. It also didn't appear while playing back in camera or in a standalone video player on the computer. I then changed a setting (can't remember which) inside Premiere and it went away. I'm hopefully that means this problem is in the past but no 100% sure. If you come across any follow-up info that might be useful please do let me know. Thanks again!


Hi Again, 
Oh that's interesting, I actually already have the Sigma 50mm f/1.4 DG HSM ART, Canon EF Fit lens.... still getting the issue! I was getting it a few times a day and then I had a shoot on sunday when I decided not to use the 50mm lens at all and I didnt come across the issue. Very interesting! 

Have you updated the c70 firmware since purchasing? (I havent yet, I wonder if that would help)

I haven't got any further updates to this as of yet but will let you know if I do! Ditto to you 🙂 

I did update the firmware for the camera as well as the adapter. 😀

ahh ok, is this after you got the error?

I may need to do this if so! 

Yes. Like I said, I haven't had the problem with the news lens since the firmware update but I did have the weird thing where it showed up in my footage in Premiere but wasn't actually there. I can't remember if I reset my preferences or cleared my cache or what, but whatever I did it fixed it and I haven't had any issues since. Good luck!

Hi again. Thanks, I will give that a try! 






I have the same problem. Did you manage to find the reason why the C70 fickler aperture?


I haven't had the problem since updating the lens firmware about a year ago. I'm guessing that's what fixed it. I don't remember exactly what the process was but I believe I went to Sigma's website and found out how to update the lens firmware there. I have also updated to the latest camera firmware since that time. So, thankfully it seems to be in the past. Good luck!

click here to view the press release