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R7 Autofocus Hunting Issue with Tamron 18-400mm Lens


I've been having consistent autofocus issues trying to use my R7 with the Tamron 18-400mm lens using the control ring EF-EOS to R mount adapter.  The lens will often work fine for the first 5-10 minutes of a photo shoot, but then it will start hunting for focus and be unable to focus on anything.  Turning the power off and back on doesn't help.  The firmware on both the camera and lens have been updated to the latest versions.  I shipped the lens to Tamron for troubleshooting and repair, and they adjusted the autofocus, but that hasn't resolved the problem.  The lens works fine on my older Rebel T4i that has the same EF-S mount as the Tamron lens so no adapter is needed.  Is it possible that the mount adapter is defective?  Or does the R7 with the mount adapter just not work properly with the Tamron lens?  According to Tamron, the R7 is supported with this lens.



Hey there!

I'd like to gather a little bit more information so that the community can better assist.

Have you tried any other lenses with the adapter? If so, which ones?
Have you tried using A+ mode to see if that works?
What shooting mode/settings have you tried? 
What focusing mode are you using?


Do you have Preview AF enabled? This works by constantly focusing the lens and may be causing the AF motor in your lens to get overused and stop working. Most lenses designed for DSLR use only focus when the shutter or back button is pressed so the motors don’t run continuously. 

EOS specialist trainer, photographer and author

I do have the Preview AF enabled.  I will try turning it off and seeing if it helps.  


 Or does the R7 with the mount adapter just not work properly with the Tamron lens?  According to Tamron, the R7 is supported with this lens.  ”

The problem is most likely the lens, not camera or the adapter.  First and foremost, the lens was designed for use on DSLRs, not MILC bodies.  Most third party lenses designed for DSLRs are not fully compatible with the advanced AF and subject tracking features found in the advanced Canon R Series camera bodies.

Disable all settings that enable eye or subject tracking.  You want to see AF points that look like grid of small AF points or boxes.  I use these setting in my R6 Mark II with the Sigma 150-600.


I recommend disabling the “Continuous AF” feature described above.  It creates an increased drain on the battery.  This feature is most useful during action photography scenarios, when the camera is almost constantly pointed toward your subjects.

"The right mouse button is your friend."

My R7 doesn't have the setting that you show in the screen shot.  Mine says "Subject Tracking" instead, and I have it turned on because I DO want the AF to detect and track the animals that I'm trying to photograph.  If I disable all of the advanced subject tracking features, I might as well use the lens with my old Rebel T4i that doesn't have those features.  The lens works fine with that camera where no mount adapter is needed since it can accept the Tamron lens' EF mount directly.  But my goal is to have the lens work with the R7 to take advantage of the R7's features.

The names of some terms does change from the EOS R7 (and EOS R10), this screen is from an EOS R7.


Subject tracking is the description used by EOS R7 in place of Whole area tracking servo AF found in the EOS R6 Mark II. 

In theory, a lens that worked on an older Rebel camera will work on the mount adapter on the EOS R7 and support the new tracking capabilities. However, it may be that the new functionalities require the Tamron lens to perform beyond its original design limitations. Tamron introduced the 18-400mm lens in 2017, some five years before the EOS R7, and at least 1 year before the first EOS R camera. Canon also has some older model EF lenses that are not able to work at the speed of the R-series cameras.

If you rented or borrowed a Canon RF lens and the camera delivers its expected performance then it would be clear that the limitation is the lens. If you send the camera and adapter to Canon to check they will only check it with Canon lenses. Canon offers no assured compatibility with third party lenses on mirrorless cameras. 

My original suggestion was to disable Preview AF how did you get on when you did this?

EOS specialist trainer, photographer and author

This morning I tried disabling the Preview AF, and found that it didn't fix the problem.  As before, the lens worked fine for the first few minutes of my walk, but after 10-15 minutes it exhibited the problem of not being able to focus on anything.  This was the case regardless of what mode I was using (A+, P, Tv, Av).  I had left the camera turned on while I was walking in case I saw any birds to photograph, and could hear the lens motor occasionally even when I wasn't using it, so maybe the subject tracking was causing the lens to keep attempting to focus on something when I was not using it.  I turned the power off for a few minutes, and after I turned it back on, the lens worked properly initially.  I kept the camera turned on and put the lens cap on to see if that might keep the AF from trying to focus, taking it off occasionally to try to focus on something as a test.  But after several minutes, the problem of not being able to focus occurred again.

All this points to a lens issue.

The way to check that is to use a Canon EF or EF-S lens on the adapter, or use a Canon RF or RF-S lens. If the camera with Canon lenses works as expected then it's for sure an issue with the Tamron lens.

EOS specialist trainer, photographer and author


Hi and welcome to the forum:

First and foremost, putting a legacy 3rd party lens is not supported by Canon.  I personally have not seen a statement by Tamron that their lenses work with the new R-series bodies, and to pursue that the correct course is to contact them.

Sigma made a statement and video that their lenses do work with the R-series bodies, but they demonstrated this only with the the FF R6 body that has a much more sophisticated focusing and tracking system then the R7. 

Quite a few people have had challenges with focus using the R7, particularly with 3rd-party lenses.   Duade Paton, an Australian photographer, spent a lot of energy on this.  While I don't agree with some of his testing methods, the telling part occurred when he sent his copy of the R7 for testing with Canon, along with sample images of his issue.

After some time and references to Japan, their response was that the camera was working as designed.  To quote from the response he read out from Canon:
We believe the autofocus issues you have presented are a limitation of the R7 capabilities.
The R3, R5, [R6] and R6MkII have autofocus speeds that are superior to the EOS R7.

AF accuracy may become unstable due to low contrast.
There is a possibility that improvements can be achieved by changing these settings:
Use H (High-speed continuous shooting) instead of H+ (High-speed continuous shooting+)
Lower continuous shooting gives more time to achieve focus thus better 'hit success rate".
Higher continuous shooting will give lower the "hit success rate"

So, what is the context to all this?  Here is my personal analysis:

While the R7 claims to have a shutter rate of 30 FPS in full electronic mode, this demands a high performance in terms of image recording, throughput and storage. Any flaw in the data bus will cause a bottleneck and negatively impact performance. I believe that in the R7 this occurs because, to me, the data bus is seriously unbalanced.

What I mean by that is that the shutter can go at 30 FPS in full electronic mode, but because the sensor is not BSI/Stacked, which would interface directly with memory and processor, it's ability to execute the recording of the image introduces significant rolling shutter effect, where a bird's wings in flight will look curved rather than natural because, as the sensor scans down or across to record, the speed is not sufficient to freeze the movement of the wings' displacement over that time. This is also seen when tracking birds in flight, where trees, poles and buildings will look tilted or round objects will look elliptical. Now, this is obviously not an issue if the birds are relatively static, but then one would ask why it is necessary to shoot at 30fps for a bird that's not moving.

Paton showed the following graph to demonstrate the relative focus speed of the R7 vs. other popular models and that it is fairly pedestrian.

The second implication of this is that the buffer is insufficient in capacity and speed for the readout of all that data coming from the sensor. This means that at 30 FPS, shooting in RAW, the buffer will fill up in about 1.2 seconds, and then you can't take any photos. This is also due, in part, to the relatively slow cards - I would have preferred to see at least one CF-Express card to allow for the fast recording speed.  It's a classic bottleneck situation.

The 32MP sensor of the R7's APS-C sensor has a pixel density equivalent to about 82MP on a FF sensor - which, as I write, no maker has attempted to achieve. As such, not only does the data output cause write issues as outlined above, but it starts to exhibit noise from about 3200 ISO, becoming noticeable at about 6400.

Furthermore, given that the R7 has a less sophisticated version of the tracking system, because the sensor is so critical in the focusing and tracking processes, the autofocus is challenged and that may be a part of the reason that people have had issues with focusing and tracking.  The camera uses the sensor photosites to achieve focus, and with the density in the R7's sensor it means that on continuous focus a lot of focus points are being engaged at a given time.  It is not unreasonable that any tiny alteration in some of those focus points at high frame rates will cause a refresh issue or pulsing focus.

I will say that the system is much more sophisticated than those of DSLRs and thus requires more study to configure and use. To be fair, I think that quite a bit of the negative feedback is from those who have not set up their systems to make the best of the technology for their specific needs and the camera's limitations.

The R7 is not weather sealed like the 7D series bodies, nor does it have a OEM battery grip - something that I really prefer with long telephotos, for the extra energy capacity, but more for the balance and the duplicate controls for shooting in portrait mode when using big leavy lenses. Again, those are my preferences and may not be relevant for you.

Now, I am perfectly aware you are shooting with the Tamron, but the lens you are using is even more ambitious in its focusing needs compared to the focal range than the Sigma 150-600 that initiated this issue.

To watch the complete video by Paton see:



cheers, TREVOR

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