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.

[deebatman316]

I would use a Canon brand EF-RF Mount adapter. 3rd Party Mount adapter cause all sorts of problems with communication issues or even causing the camera to lock up. All I've found that the further apart 3rd Party gear is to a new camera. Often times incompatibilities do arise due to the age difference and cameras available at the time. Canon DOES NOT tell 3rd Parties how their lens communication works. Instead Sigma must reverse engineer their lenses to work on the EF Mount. Canon only ensures compatibility with their own gear they released not 3rd Party gear. Canon didn't make or design the 3rd Party item so compatibility falls to Sigma who has claimed compatibility with the EF Mount.

[shadowsports]

Greetings ,

Based on the culmination and recent experiences of many, we have noticed that the R7 can be particularly finicky with third party glass.  Works very well with some, but not all 3rd party gear.  In some cases, firmware upgrades have helped.  Primarily with sigma's global vision lenses (contemporary, art and sport).  

I don't think it's something that was done deliberately, but rather something that's just part of that body's DNA.  

Of course, the information Demetrius has provided is 100% accurate.  Using authentic Canon adapters is the way to go.  While Meike and Viltrox are popular. Their compatibility has also been hit and miss.  In many cases, some older lenses just don't work.  Either as well, or as fast, etc.  I feel Canon is continually improving the communication algorithm of the RF Mount.

The sigma compatibility tool doesn't appear to show support for this lens on the R7. It's a good one but is now 12 years old.  

Camera Compatibility | SUPPORT | Sigma https://share.google/3UdMMNnsrjimq8Wm5

I have owned many Sigma lenses and have been very pleased with their performance, but I did fully migrate to RF shortly after moving to mirrorless.  I started slow and then pulled the trigger.  I know it's difficult, especially after you've owned something for a while, become very familiar with it and rely on it so much.  

I'm not suggesting you run out and buy the the RF100-300.  It's quite an investment and is really geared to a professional or someone with business justification and the capability of tax incentives 😂. Who knows, maybe someday.  

I think about the closest you'll get in quality and performance (favorable price point) is the RF 70-200 f2.8 Z.  

[JamesMedia]

I did use authentic Canon adapters. along with 3rd party adapters. 

[JamesMedia]

Clearly neither of you two read that I did use Canon adapters.  I only mentioned the 3rd party adapters to cover my bases.  

[deebatman316]

Yes I did see that I just wanted to point out the importance of sticking with the OEM Mount adapter. As more features come to the RF Mount. 3rd Party lens compatibility could be broken. This is not done in spite by Canon. Canon could easily use or change a piece of existing code and break 3rd Party compatibility. Or use a piece of code previously not used but was supported the whole time. But their existing lenses remain compatible and remain unaffected. Canon has in the past made changes to EF Mount communication several times. One thing to note is that as new faster cameras have been released. Canon has had to increase the communication speed between the lens and the camera. Older slower 3rd Party lenses cannot keep up with the increased communication speed. But older cameras would work fine with those older 3rd Party lenses. In 1987 the EF Mount was released with Arc Form Drive AF motor lenses and Ring Type USM lenses. In 1992 Canon replaced Arc Form Drive with Micro Motor. When this change happened Canon also changed how AF & Aperture control work. This broke compatibility with 3rd Party lenses. Fast forward to 2004 digital cameras are the new thing. Also The EOS-1D Mark II & E-TTL II are released. This again breaks compatibility with 3rd Party lenses due to the lens drawing to much power for the aperture motor. In 2009 the EOS 7D (classic) is released so is Dual Pixel Autofocus (DPAF). 3rd Party lenses wouldn't AF in live view or movie mode. Canon refined there new lenses to be compatible with it. In 2012 EOS M was released and compatibility was broken again with 3rd Party lenses. Incorrect exposures would happen sometimes up to 3 stops overexposed or the lens wouldn't AF. Also in the same year Canon would release the EOS-1DX (classic). This camera could shoot up to 12 fps which no other DSLR camera at the time could shoot. Canon had to speed up communication with the new lens to achieve this. Old lenses couldn't support this high shooting rate and the camera would slow down for older EF lenses. In 2018 Canon releases the RF Mount and the original EOS R camera. Also Canon changes something in the E-TTL flash system. 3rd Party flash compatibility is broken and user find their cameras locking up with error 70. Canon changed the AF Assist Beam signal that the camera sends to the flash. Since the IR AF Assist Beam is INCOMPATIBLE with mirrorless cameras. So Canon reused code to allow their speedlites to use Intermittent Flash Firing for the AF Assist Beam. 3rd Party speedlites would see this command and fire a pre-flash and lock up the camera. In 2020 the R5 & R6 were released and 3rd Party mount adapters cause cameras to lock up. 

[Waddizzle]

If the Sigma doesn’t work with the R7 and Canon adapter, then the lens firmware may need an update.  As old as the lens is Sigma may no longer support the lens. 

[JamesMedia]

My apologies.  I didn't realize that this type of thing was ongoing.  I am hoping for a firmware fix or something simple,  other than spending 10K for a new comparable lens. 

[deebatman316]

I would contact Sigma about possible new firmware updates for your lens. Remember anytime a new camera is released. There may be changes in the lens or flash communication protocols. I tell people this all the time. New features mean that Canon may have to write new code for those new features to work. Especially with cameras that shoot high fps In stills mode usually 12+. Lenses have to be designed for that and the communication speed can’t be slow either. Remember Canon is the one who made the code. So they know how it’s supposed to work. That’s how they can have seamless compatibility between old and new gear. Even if the lens was released in 1987 and adapted to the newest EOS R series camera of today. Even if there are some limitations with the gear combination. 

[JamesMedia]

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

Just to clarify, I did reach out to Sigma about this lens compatibility issue and I’m currently waiting on their response via email. I provided them with detailed information, including the fact that this same Sigma 120-300mm f/2.8 EF lens works flawlessly on both of my Canon R6 bodies and my M50. It’s only the R7 that throws the Err01 error.

I'm hopeful that Sigma will be able to provide some insight or possibly a firmware based solution, though I also recognize the challenges they face without access to Canon’s internal mount protocols.

In the meantime, I’ll continue documenting this in case others run into the same roadblock. Thanks again for taking the time to respond. I do appreciate the conversation and the knowledge you all have shared. 

-James