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

Discussion in 'Canon Cameras' started by Slavuta, Jun 23, 2020.

  1. Slavuta

    Slavuta TPF Noob!

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    Hi!

    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.


     
  2. zombiesniper

    zombiesniper Furtographer Extraordinaire! Supporting Member

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    Since this seems to happening at specific focal ranges it would lead me to believe that it could be the cuircut board (thay are flexible ones) may be having an issue or a separation at some point. When you turn the zoom ring in the right spots the AF will work but in other spots it won't.
    I have seen this type of abrasion to flexible circuits at work.

    I would reccomend having it looked at by a good repair facility and then based on their findings go from there.
     
    • Agree Agree x 1
  3. Derrel

    Derrel Mr. Rain Cloud

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    Idea: you got four years of use of of it...get another lens like it or similar to it.
     
  4. Slavuta

    Slavuta TPF Noob!

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    @zombiesniper, thanks for your feedback. Interesting. So there are circuits inside the lens that may have just certain sections go out of wack, leading to the autofocus to consistently fail only across predictable segments? That would make sense. Hopefully that's what it is. Now the trick will to locate an adequate facility to take a look inside. I'll report back on whatever findings for anyone else's future reference.
     
  5. Slavuta

    Slavuta TPF Noob!

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    Well that's not much of an idea -- more of a last resort. Four years is not a normal life span for a lens, and there's no reason to chuck out a piece of optics as soon as it develops a problem. Repair is the cheaper and more sensible option, which is my next step. I was just curious to see if anyone else has had this happen.
     
  6. Derrel

    Derrel Mr. Rain Cloud

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    You wrote "any ideas or feedback would be appreciated." So much for that being true, eh?

    I gave you a solid idea. It's an idea based upon the type of lens and the original selling price, and upon typical repair vs replacement costs based on decades of experience. Your idea that repair is the cheapest option is in many cases not true at all . The lens you had is not that expensive...I expect repairs and shipping will total at least 450 Euro/Dollars. Do you think you can find a replacement 28-300 for less, or would it be more?

    Do you think you could get the lens to a qualified repair facility for a written estimate? That would be step one; get the problem diagnosed, and repair options sent to you. If repair is affordable, then go the repair route, otherwise look into a used replacement, or a substitution of another comparable superzoom.
     
    Last edited: Jun 25, 2020
  7. Derrel

    Derrel Mr. Rain Cloud

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    20200625_101410.jpg
     
  8. Slavuta

    Slavuta TPF Noob!

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    I'll attempt to get it fixed it locally (in a cheap neck of the world I'm in now). Whether they can successfully futz with the insides of a zoom lens remains to be seen. Otherwise, I may just wait till I hit the US and can hand it over to an affordable but competent repair shop.

    This is the only walk-around lens for full-frame Canons; there's no good alternative. At any rate, gonna see about getting it fixed b4 giving up on it.
     

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