[UncleVanya]

Auto focus repairs to SDM lenses are well known to be short-lived. I hear there's a version 2 of the 16-55mm coming out some time soon but the whole DA* range of lenses is well overdue a re-design, more than anything to fix the AF problems.

While some have had no problems with these lenses, many people have. I just avoid them, which is a shame because there are some I'd really like to have.

With the exception of the 60-250, all of the ones initially released 16-50, 50-135, 200 and 300 are fine when converted so the risk isn't that bad. The 16-50 however has not the best optics on the wide end and needed a serious look from Pentax. The 60-250 is probably largely irrelevant due to the 70-210 f4. The 200 probably needs a redo, it's basis is an older film design and it suffers from a bit of ca. The 300 and the 50-135 are excellent optically but they are slower to focus than some would like to see. If the optics could remain unchanged and faster focusing was achieved I'm sure we would all be happy to embrace changes.

However if you look at it like me, those lenses are a fantastic bargain today. Get one with a bad sdm motor and convert it and enjoy it.

My theory on lenses with multiple repairs is that something in the lens or the environment (camera perhaps?) is not getting addressed during repair causing another premature failure.

[UncleVanya]

I would happy defer to your far greater experience

My experience could be biased by the ones I'm sent. And the ones sent might be biased by the users love of the lenses - maybe they want the 50-135 repaired more because they love it so much?

But some of my opinion is just observational, and without great statistics available we are all ultimately guessing.

[jddwoods]

Not by any means. The DA*200 and DA*300 have SDM as well. Of the DA* lenses, the 16-50 and 50-135 have by far the worst reputation for failure, with the 60-250 a distant third. It least that's my impression.

I don't own it, but I gather the DA17-70 has SDM too. More reliable though.

Other lenses with nominal SDM AF, like the Tamron-designed DA18-270, DFA15-30 and DFA24-70, should not be tarred with the same brush.

Actually the 17-70 has one of the highest incidences of SDM failure and also it cannot be converted to screw drive. Mine failed a few years ago and I would like to get it fixed but I have seen too many reports of repeat SDM failures after new SDM motors were installed. I would go for the fix if I could have confidence the new motor would be more reliable.

[Wheatfield]

So I have a few questions.... I bought the SMC-DA 50-135 lens back in 2011. In 2014 it would not focus at all in AF so I sent it to Precision for repair. Worked fine until this summer and now it won't Auto Focus again. Sent it back to Precision and to repair this time they quoted me at $526. Looked on Amazon and new they are selling for $700. My first thought is just to buy a new one However, what are the chances the new one will have to be repaired too? Has Pentax done anything different with more recently manufactured lenses to keep them from having this problem? Am I better off with a new lens and chance it having issues at some point? Or better off with a lens that has been repaired (twice) ?

Unfortunately, the 50-135 has a bad AF. It's been suggested that you hack it into a screw drive AF lens, and this is the best advice there is.

[UncleVanya]

Actually the 17-70 has one of the highest incidences of SDM failure and also it cannot be converted to screw drive. Mine failed a few years ago and I would like to get it fixed but I have seen too many reports of repeat SDM failures after new SDM motors were installed. I would go for the fix if I could have confidence the new motor would be more reliable.

This is my impression as well but I lack data. I recall when I first got into Pentax DSLR's my father's best friend who worked for Pentax as a sales rep told me to stay away from the 17-70. However I got a great deal years later and took the chance. My copy was refurbished and has never had problems since. I suspect mine was refurbished later in the lifecycle of SDM and may have the improved motor which while not perfect seems more reliable. On the other hand my step niece hasn't exactly taxed the lens with excessive use - she's an infrequent photographer.

[Fluegel]

The 16-50 was not strong in the WA range so I avoided that lens. I am perfectly happy with the Sigma 17-50 HSM lens.
Wonder why Pentax did not put in more effort to correct the design flaw with SDM equiped lenses. It is strongly against the Japanese habit that products should function well.

A Japanese factory based in the UK produced loudspeaker cabinets. For packing they contracted a local company that produced carton boxes.
The sales rep of that company was invited to discuss a problem with the boxes. There were three boxes in the office of the person who was responsable for quality control. He pointed out what the problems were.

That can easily be solved, we will send you three new cartons. The Japanese gentleman answered the solution is not that simple.
We expect all boxes to be perfect. We do not accept products that do not meet our quality standard. They had over 100.000 of those boxes and wanted each of them to be perfect.

[leekil]

My own impression is slightly different. I would rank the failure rate of the 16-50 and 50-135 similar to Sandy. But the 300 would be next on my list followed by the 60-250 then the 200.

In my personal experience, the 16-50 has been the worst, the DA 55 second, and the 50-135 is great!