[ChucK20D]

Howdy Pentaxians;

I have an SMC Pentax-DA50-135 ED [IF] SDM lens I bought on MPB.

The focus motor worked for awhile but then finally conked-out.

I'm currently thinking about the 2 options for reviving it.

• Option A: Convert to screw-drive $000.00
• Option B: Replace the faulty SDM motor $450.00 (approx. as I understand it).

Option A is VERY unappealing as I've been working to get away from screw-drive lenses which I dislike very much.
Option B is reasonable because I only paid about $375 for the lens to begin with for a 1k lens.

So here's my question; has anyone done Option B?
Are the new SDM replacement motors more reliable than the originals?
Needless to say, doing the replacement is only worth it if it's an improvement.

Thanks,

Chuck

[AstroDave]

ption A is VERY unappealing as I've been working to get away from screw-drive lenses which I dislike very much.
Option B is reasonable because I only paid about $375 for the lens to begin with for a 1k lens.

So here's my question; has anyone done Option B?
Are the new SDM replacement motors more reliable than the originals?

Why is option A so unappealing? I am happy with ALL of my old-fashioned screw-drive focussing lenses. So, they are a bit noisy - just live with it.

As to B: I have a vintage 16-50 lens which was replaced many, many years ago (more than 10) for a focussing problem, which I did not recognize what it probably was then (I'm not sure Pentax USA recognized it either), but was probably the SDM, and I was using that lens just this morning and the focussing was just fine. So, many years later, the fix/replacement works perfectly.

[UncleVanya]

I have converted at least 100 lenses if not more. Two observations- many of my customers have replaced their motors before it failed again. Many people - myself included have had lenses with original motors or replacement motors without these failing. I theorize that something in the lenses that fail repeatedly is at fault beyond just the sdm motor. In some lenses the updated replacement works great without further failures - despite the user accounts of how they use them is similar.

But it’s only an observational theory. I have no way to randomly assign lenses and test. It’s possible something the users of lenses that repeatedly fail do in their handling of the lenses that contributes to failure. I can say that theories about non-use don’t seem to be applicable universally - as some of my sdm lenses sit for long periods idle without failure (so far).

[bschriver11]

I would convert mine to screw drive without giving it a second thought. The SDM lenses seem kind of hesitant to lock focus and hunt sometimes which i don't see in my screw drive lenses, i often wonder if my DA* 50-135 might focus better converted?

[AlwaysAl]

Seemingly same path, got the 50-135used for a good price. It had had a motor replaced and documentation was provided. Motor failed within a few months (erratic at first, then nothing) and was out of repair warranty. Replaced the motor assuming the newer motors were better. Motor failed again, converted to screw drive...it works reliably now.

[UncleVanya]

I would convert mine to screw drive without giving it a second thought. The SDM lenses seem kind of hesitant to lock focus and hunt sometimes which i don't see in my screw drive lenses, i often wonder if my DA* 50-135 might focus better converted?

Hesitant and focus lock hard to achieve suggests declined sdm performance. Good sdm doesn’t do that in my experience.

I’ve converted a few lenses with that kind of symptom. All the customers reported it fixed the issue.

---------- Post added 12-20-22 at 11:57 PM ----------

Seemingly same path, got the 50-135used for a good price. It had had a motor replaced and documentation was provided. Motor failed within a few months (erratic at first, then nothing) and was out of repair warranty. Replaced the motor assuming the newer motors were better. Motor failed again, converted to screw drive...it works reliably now.

Those horror stories are few but not zero. That’s what makes me wonder what else might be involved. Why are some lenses just fine and others are serial failures.

[AfterPentax Mark II]

Those horror stories are few but not zero. That’s what makes me wonder what else might be involved. Why are some lenses just fine and others are serial failures.

Perhaps it is the same story like those about Toyota: different suppliers for the same parts of the lens, excluding the lenses? With Toyota we saw that some models of a certain line had problems and Toyota found out that it had to do with the supplier and its failing QC. Just a guess.

[ChucK20D]

Why is option A so unappealing? I am happy with ALL of my old-fashioned screw-drive focussing lenses. So, they are a bit noisy - just live with it.

As to B: I have a vintage 16-50 lens which was replaced many, many years ago (more than 10) for a focussing problem, which I did not recognize what it probably was then (I'm not sure Pentax USA recognized it either), but was probably the SDM, and I was using that lens just this morning and the focussing was just fine. So, many years later, the fix/replacement works perfectly.

Dave;

I dislike the racket that screw-drive makes. Just bugs me. Given the potential for further unreliability with a new motor, I may just go with the screw-drive conversion. But not without grumbling.
Leaving the auto-focus non-functional is definitely not an option for such a nice piece of kit.

[DAKS]

I had one of the early 50-135 SDM. It died at the worst possible shooting moment. I sent it back for repair. It has worked fine since then, but, frankly, I still don't trust it and am hoping for a 50-135 PLM replacement. If you don't want screw-drive, a replacement motor would be a good deal, but there's not counting on how long it will last. What kink of warranty comes with the new motor?
I've had good luck with my replacement. Is there any data on how quickly replacements fail if they do?

[ChucK20D]

Daks,

Re survival data for replacements, good question. I sure would like to know before I make the decision to replace the PLM in mine.

[UncleVanya]

Dave;

I dislike the racket that screw-drive makes. Just bugs me. Given the potential for further unreliability with a new motor, I may just go with the screw-drive conversion. But not without grumbling.
Leaving the auto-focus non-functional is definitely not an option for such a nice piece of kit.

If it helps I think the AW lenses aren't as loud as the normal screw drive lenses. I can try to do a comparison video at some point. It isn't silent that is certain. My own lens is a refurb from Pentax HQ (we think) it was bought after the closing of the HQ in Colorado from a vendor in that area. I have never had any trouble with it but I have no history - it was sold with NON-Working SDM - but a vigorous exercise of the manual focus using a method that had been discussed but not done by a number of people was all it took to wake it up and it has never gone back to sleep. Weird but true. I have converted it at times - originally to test the method - occasionally for the purpose of a diagnostic check on a possible issue for a customer with a lens that they wanted to convert, but largely it stays set to SDM and just works.

Does this mean all repaired lenses work well - clearly not. I don't know if anyone has statistics. I have heard from multiple failure owners - probably because they are frustrated and my conversion service is cheap and reliable. (Self-Conversion is encouraged - I just provide the service to help those who don't want to mess with it or lack the needed vintage gear.)

[ChucK20D]

UncleVanya;

Re "vigorous exercise of the manual focus" I discovered that wake-up method when mine started getting balky. It worked well for a little while, until it went DOA finally. That the method works with a new SDM installed suggests there's another issue that contributes to the SDM malfunction.

Re screw-drive conversion; do I understand correctly that once the lens is converted, it can still access the SDM?

Thanks,

Chuck

If it helps I think the AW lenses aren't as loud as the normal screw drive lenses. I can try to do a comparison video at some point. It isn't silent that is certain. My own lens is a refurb from Pentax HQ (we think) it was bought after the closing of the HQ in Colorado from a vendor in that area. I have never had any trouble with it but I have no history - it was sold with NON-Working SDM - but a vigorous exercise of the manual focus using a method that had been discussed but not done by a number of people was all it took to wake it up and it has never gone back to sleep. Weird but true. I have converted it at times - originally to test the method - occasionally for the purpose of a diagnostic check on a possible issue for a customer with a lens that they wanted to convert, but largely it stays set to SDM and just works.

Does this mean all repaired lenses work well - clearly not. I don't know if anyone has statistics. I have heard from multiple failure owners - probably because they are frustrated and my conversion service is cheap and reliable. (Self-Conversion is encouraged - I just provide the service to help those who don't want to mess with it or lack the needed vintage gear.)

[UncleVanya]

UncleVanya;

Re "vigorous exercise of the manual focus" I discovered that wake-up method when mine started getting balky. It worked well for a little while, until it went DOA finally. That the method works with a new SDM installed suggests there's another issue that contributes to the SDM malfunction.

Re screw-drive conversion; do I understand correctly that once the lens is converted, it can still access the SDM?

Thanks,

Chuck

The reason I suspected it might help is stiction can be an issue and the low torque of the sdm motors makes this seem more likely. The lens was listed as refurbished but sdm not working. I took a chance that it was just stuck. Luckily it proved to be a good gamble.

[Grokh]

The engine of my 50-135 failed three times.
In the end I just converted the lens into a screwdriver.

[ChucK20D]

The engine of my 50-135 failed three times.
In the end I just converted the lens into a screwdriver.

Grokh, do you mean 2 SDM replacements failed?