I've read many reports that the SDM autofocus motor in some Pentax lenses may stop working after several months or years of use. Why does this happen, and is there anything I can do to prevent failure or restore a lens with a failed SDM (aside from sending it in for repair)?

  • I've heard (from people on the Internet) that it's a good idea to use the lens frequently. But I'm not sure that there's any evidence for this belief, aside from anecdotes by people who took a lens out of storage and found the SDM to not work anymore. – coneslayer May 26 '12 at 1:01
  • Keep in mind I'm on Pentax Forums, so I'm well aware of this. I'm trying to understand precisely what's wrong with the SDM when it fails and what other solutions may exist. – bwDraco May 26 '12 at 1:04
  • Both my lenses which failed the SDM were extensively used, so I doubt lack of use would have done it. I have two lenses which I use less often and they did not suffer SDM issues. Regardless, this is a small sample and we would need to have thousands of data points to conclude anything. – Itai May 26 '12 at 3:58

When 2 of mine failed, the solution was the same: Send it back to the manufacturer. Once it was under warranty, the other time it was not. Pentax is notoriously slow at servicing parts and, sadly, it took between 2 and 4 months to get the lenses back.

These were some of their earliest lenses which had more problems. This has not happened with any of my newer lenses. Not sure if there was anything to do other than not use autofocus. It seems like a wear-and-tear issue because before mine failed, the AF was getting slower and slower on one lens and on the other it stopped working for certain distances. Eventually it stopped completely. Now since this was in the K20D times, maybe I would have just used MF for the out-of-warranty one, it is easy to focus faster than a K20D by hand :)

My first lesson learned here was that if you have a backup camera body, a lens eventually fails. Since then, I have both backup bodies and backup lenses.

2016 Update

Four years later, those same two lenses, now both over 8 years started to have intermittent issues. As they are still optically perfect and I cannot part with them for a while, I decided to hack the firmware of a lens and do it to the other, if it worked. The good news is that it worked flawlessly and now these two lenses focus again quickly but not as quietly. None of the newer lenses ever had issues, so it must be a first-generation thing. This video explains it perfectly.

  • In Canada, where do you send them? Is there a single North American repair center? For us in the US at least, it's outsourced to CRIS. – mattdm May 26 '12 at 1:12
  • @mattdm - You'd send them to Pentax Canada, the office is in Mississauga (just outside of Toronto) and they would either fix there or, more likely, send it to Japan. My experience wasn't too bad, but they're only a half hour away for me. – John Cavan May 26 '12 at 2:09
  • They almost always fix them now in Mississauga and this shorted the time somewhat I was told but I still avoid doing non-essential fixes. – Itai May 26 '12 at 3:00
  • @Itai - My K-5 was sent to Japan for repairs, though I think they ended up doing a body swap at the time. That was for the infamous sensor stain issue though, so I suspect they had little choice. – John Cavan May 26 '12 at 3:12
  • @John - Yes, I did say almost :) The serial number was different on the first lens I sent, so yes sometimes they swap the whole thing. You should be able to check that with your records. – Itai May 26 '12 at 3:17

An answer that might help you is what I did when one of my lenses failed. I still use the K10D body and so I reverted to an earlier version of the firmware (1.2). This forced the camera to use all SDM lenses as screwmount. If you have a K10D body that hasn't been updated to 1.31 firmware, you can revert via a hex hack.

This is the only way that I know to still use AF with the SDM lenses when they fail.


I would say you can convert the lenses into screwdrive and you will have auto-focus again. I did that with a Pentax DA* 50-135mm f2.8 with a dead SDM and it auto-focuses now with the screwdrive.

The solution is known in case you decide to try it by yourself.

It is quite easy to do. You just need to follow the steps, be patient. It should take around 15 to 20 minutes of your time and you will have again a fully AF lens.

In my case it made an SDM lens that previously would not auto-focus work again without any issues.

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