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Autofocus not working on Tamron 28-300mm VC PZD lens for Canon

Slavuta Avatar
Slavuta 3 1
22 Jun 2020 8:06PM


I'm suddenly experiencing an auto-focusing issue with my Tamron 28-300mm Pzd VC f3.5-5.6 lens for full frame sensor cameras (Canon mount). I've never encountered this before with this or any other lens. And there was no gradual deterioration: from one day to the next, autofocus just started failing. Wondering if anyone has run into something similar and/or may have some ideas as to the cause (and the cost of repair).

Here's what's happening. The auto-focus on this lens no longer properly works across the focal length range of roughly 33-40mm and 120-300mm.

Across the ranges of 28-33mm and 41-120mm, the autofocus appears to work just fine, the way it always has. (Note, all ranges are obviously approximate, but pretty close.)

However, for any focal lengths in 35-40mm, AF is not working at all: meaning that the lens doesn't even react when I press the focus button on the camera (in my case, programmed to the back-focus button). The focus motor doesn't appear to engage, and no attempt at focusing is made. There's no sound, no shift, and no change to the focal plane of the image.

For any focal length past about 120mm, the autofocus varies from barely working to not working at all. Meaning that it laboriously shifts the plane back and forth a few times and finally locks on something close to focused but not quite. Or it shifts back and forth randomly a few times, repeatedly sailing way past the right focus, and finally locks it incorrectly -- on a totally blurry image. Curious thing to note is that at any one given focal length it may kinda-sorta lock correct focus for an object at one distance and not at all for another distance.

But one thing for sure, the AF is now consistently faulty across those segments of 34-40mm (where AF fails to react at all) and 130-400mm (where it searches on and on and fails to lock the right focus).

Right away, here are the troubleshooting steps I've already tried, to no avail:

- Manual focus works fine. The lens gear rotates normally as per usual. Nothing seems stuck or dislodged or missing.
- I took off the lens and put it back on a few times, to make sure it's properly mounted.
- The contacts on the lens and camera (Canon 6D ii) look clean and intact.
- I've played with toggling back and forth between AF/MF and having VC (stabilizer) in ON/OFF position. There are no other buttons/switches on the lens.
- The lens is in fine condition. There's a minor amount of dust to the insides of the optics from four years of frequent use, but no major impurities. The back end seems quite clean and in good condition. There's one cosmetic defect to the outside of the lens: the ribbed rubber gear covering the focus ring has become stretched out overtime and hangs a bit loosely, but this of course should have no effect on the internal function of the autofocus.
- I've reprogrammed the customizable buttons on the camera a few times, assigning focus to various ones.
- I've tried out different focusing settings, e.g. single point, cluster, zone, etc. I've also compared focusing through viewfinder vs. using LCD display, as well as with focusing button vs. via LCD touchscreen.

None of the above had any effect whatsoever on the problem. It remains quite consistent. The same AF failure keeps occurring across the same focal length ranges.

- My other lens (a prime) continues autofocusing just fine.

Since I have no other telephoto lens with me and no other camera, I'm not able to definitively narrow this down to a lens problem as opposed to a camera one. But everything points to it being a lens malfunction.

Any ideas or feedback would be appreciated! Cheers.
LenShepherd Avatar
LenShepherd 15 4.7k United Kingdom
23 Jun 2020 8:57AM
As your other lens continues to work as it should the problem is unlikely to be with the camera body.
If you have not already done it try carefully cleaning the electric contacts on the lenses bayonet and also in the throat of the camera body.
This resolves many but unfortunately not all autofocus problems.
If this does not solve the problem it would seem best to send the lens back to Tamron for a repair.
Slavuta Avatar
Slavuta 3 1
23 Jun 2020 4:12PM
Yeah, I think I'm gonna have to, LensShepherd.
Was hoping to find some reports of similar problems (and fixes) to get an idea of what may have gone awry with it. But thus far -- crickets. Guess it's an uncommon issue.


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