Canon R7 and Sigma 120-300mm F2.8 compatibility issues

[JamesMedia]

I’m trying to determine if anyone else has run into this or found a fix. I use a Sigma 120-300mm f/2.8 DG OS HSM (EF mount) — works beautifully on both my Canon R6 bodies and on my M50 (using EF to RF or EF to M adapters).

However, when I mount the lens to my Canon R7 (via Canon, Viltrox, or Meike EF-RF adapters), I get an Err01 communication error. No aperture or focus response, and the lens isn’t recognized at all. My Sigma 85mm EF works fine on the R7 with the same adapters, so this seems isolated to the 120-300.

All firmware is updated. Contacts are clean. I've tested multiple batteries and adapters. The lens still works perfectly on my other bodies.

When I called Canon support, the rep walked through some basic steps, but ultimately suggested I "just buy the Canon RF 100-300mm f/2.8." I mentioned it’s $10,000+, and he was surprised — looked it up and said, “My God, yeah it is.”

I’m not here to stir anything up, but I can’t help but wonder if this is a compatibility oversight or something more deliberate.

Has anyone else had this issue? Is there a workaround? Or do we know if Canon is addressing EF lens compatibility quirks like this?

Thanks in advance for any help or info.

[Waddizzle]

“ Thanks, Demetrius, I appreciate the additional explanation and the background on Canon’s evolving communication protocols. “

I am sorry to hear about your experiences.  Does this happen with other EF mount lenses with the R7?

I am uncertain what you mean by that comment.  The communication protocols for the EF mount have not evolved.  Your lens has an EF mount. 

I can only guess as to why your lens works on this RF camera body, but not that camera body.

 I would try turning off OS on the lens, as well as switching the lens to MF before powering up the camera.  

You do power down the cameras before you mount or dismount a lens, right?

You do support the weight of the lens at all times, right?

[shadowsports]

Hi jamesmedia, we absolutely read your post and did note that you had tried with a Canon adapter, but unfortunately it doesn't mean the lens will work.  

[JamesMedia]

Hi Rick,
Yeah, it’s definitely frustrating. I’ve asked around quite a bit and tried every suggestion people have offered, but no luck so far. My R7 works with every other EF and RF lens I own, both Canon and third-party, including Sigma, Laowa, and Rokinon. The only lens it refuses to work with is the Sigma 120-300mm, which ironically was the entire reason I bought the R7 in the first place.

Now I’m left with a camera that feels borderline useless for what I actually intended it for. I suppose that’s not entirely fair, it does work with my Laowa 100mm macro lens, though that’s an RF mount and fully manual. It’s more of a niche tool, but still kind of fun to use.

[nahpungnome]

I updated my R7 to 1.7.1 from 1.4.0.  I was able to use my 120-300 Sport on 1.4.0, but after updating to 1.7.1, the camera doesn't recognize my lens at all.  It behaves as if it's a fully manual lens with no electrical contact.  No errors or anything like that.  My 150-600 Sport still works fine.  My 120-300 works fine on my R...I'm trying to figure out a way to downgrade my firmware safely, but it doesn't seem like I can.   

[nahpungnome]

I sent Sigma an email (info@sigmaphoto.com) about the issue.  They said I'd need to send in the lens to match the firmware.  I'm not sure if this is just some canned message or they can actually do something to make it work with my camera.  Either way I'm not going to send it in, I'll just use it on my R and 7DmkII if needed.

[JamesMedia]

Same.  I can't risk my lens getting damaged or lost in transit.  Nor am I going to risk it coming back and not working with any of my cameras. I was hoping someone had an answer.