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07-04-2017, 08:45 PM   #1
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SDM issues, real or imagined

I have read differing opinions about the use of SDM in DA* lenses. My experience with both DA* 16-50 and DA* 60-250 is that both have had their SDM motors replaced twice within 3 years. The first issues happened within the warranty period of 2 years ( I live in Canada ).

One comment that I have read about is that the capacitor needs to be charged but I had a lens meltdown in the middle of a far away trip where I had been using this lens extensively for days when it suddenly would not operate, even in manual mode. In all 4 instances, the authorized repair facility advised that the SDM had malfunctioned. In the last repairs to each, a new version of the SDM was installed. Replacement costs were around $300 each time.

What recent experiences have others had?

I now have added new D FA lenses: the 100 WR, the 70-200 and the 150-450 and find the last particularly wonderful. I am using these on a K3. Like many, I suspect, I have switched to the DFA designation in anticipation of sometime adding a K1 to the mix.

07-04-2017, 09:24 PM - 1 Like   #2
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A quick search of the forum will bring up numerous threads about SDM issues. Some of them pages and pages long. I suspect most issues have been similar to yours. And the statement from Ricoh was new build lens are using a different mechanism. For whatever reason, SDM complaints have almost completely disappeared compared to back a few years. In 2014-2015 about it seemed half the threads on this forum were about SDM. Perhaps by now all lenses in the affected block have been replaced, or repaired. Who knows, but the volume has died off from a flood to a bare trickle. Not fun for those that still have issues but no longer the huge issue it was back then.
07-05-2017, 03:08 AM   #3
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QuoteOriginally posted by Yoda boy Quote
One comment that I have read about is that the capacitor needs to be charged.
Sigh... there is no capacitor which "needs to be charged" for minutes. It's an idea started by some Youtube clown, who doesn't have a clue what a capacitor is/does. Please, don't propagate such nonsense!
If you think I'm exaggerating, ask an electrical engineer and watch his reaction. He might even be able to make a gross estimation of the capacitor's size - necessarily much larger than the flash one (which only needs seconds to fully charge!).

Just a few ideas:
- no electric motor needs a "jumpstart" from a large capacitor to start moving.
- if it would need such a jumpstart, it would need it every single time. That means a minutes-long pause before every AF motor movement. Believe me, you would notice that!
- there's no way you'd miss such a large capacitor, if you open up a lens. Probably even if you don't open it up, as there would be a bulge housing it.
- discharging a powerful capacitor through a micromotor would literally burn the micromotor, I'd say. Those things are dangerous.

About the SDM issue:
Unfortunately, those two lenses - the first SDM lenses - were known for this, especially in the first years. Now the number of reported issues seems to be fewer.
Pentax took their time in updating the motors.
(FTR, my only SDM lens - DA* 60-250 - worked fine until I sold it; I think - but I'm not not 100% sure - it used the new type micromotor from the beginning)
07-05-2017, 06:07 AM   #4
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Long live screw drive?

07-05-2017, 06:41 AM   #5
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QuoteOriginally posted by Kunzite Quote
Sigh... there is no capacitor which "needs to be charged" for minutes. It's an idea started by some Youtube clown, who doesn't have a clue what a capacitor is/does. Please, don't propagate such nonsense!
Then what is the explanation for the fact that the camera must be on for a minute or two before SDM starts to work?
07-05-2017, 06:58 AM   #6
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First, lack of better knowledge is not proof to support the first theory you can think of (or - in this case - you're told about by someone on Youtube).

Second, the capacitor theory it's an impossibility, a nonsense. Please read my previous post. Please take my advice of asking an electrical engineer, which should know a thing or two about capacitors and piezo motors.

Third, what you claim to be a fact is not: only in some instances, the lens would start focusing after a few minutes or so. A properly working SDM lens would not need such a "warm-up time"; mine never did. And if if happens, most often that's a sign that the SDM motor is about to fail completely.
To be fact, your claim would have to be consistent - including a "lens charge" being mandatory and described in the manual for each newly bought SDM lens (because they would reach you "discharged"). Lens repair manuals would describe how to discharge the dangerous (and invisible) capacitor.

I'm amazed how you can ignore all those inconsistencies.

By the way, stiction is a frequent cause of failure in piezo motors.

---------- Post added 05-07-17 at 04:59 PM ----------

QuoteOriginally posted by timw4mail Quote
Long live screw drive?
DC is fine. PLM is "only" one year old, but so far, so good.
07-05-2017, 07:09 AM   #7
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I haven't claimed anything. Just asked a question...
07-05-2017, 07:24 AM   #8
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"the fact that the camera must be on for a minute or two before SDM starts to work".
It's not a fact; it's something that happens in a few instances, before the lens fails completely.

07-05-2017, 08:26 AM - 1 Like   #9
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QuoteOriginally posted by Kunzite Quote
"the fact that the camera must be on for a minute or two before SDM starts to work".
It's not a fact; it's something that happens in a few instances, before the lens fails completely.
It is a fact that my lens have behaved this way for the last 7 years.
07-05-2017, 08:31 AM   #10
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That's a sample of one, something you never mentioned before.
I've made a pretty strong case against this nonsense theory, could we stop here?
07-05-2017, 08:33 AM - 1 Like   #11
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QuoteOriginally posted by Pål Jensen Quote
Then what is the explanation for the fact that the camera must be on for a minute or two before SDM starts to work?
I'd suspect:
1) differential thermal expansion of the piezo elements and rotor
2) mechanical release of stiction from the forces induced by trying to get the lens to work

The "capacitor" story makes no sense both at the level of how electronics works (only extremely large capacitors take more than a few seconds to charge) or how non-defective SDM lenses work (non-defective lenses that have been sitting don't need charging time).

P.S. If a given user has suffered repeated SDM failures, I'd also suspect that something else is contributing to the lens failure. It could be a electrical problem in the camera that is either damaging or under-powering the SDM mechanism. Or it could be that the user's pattern of use of their lenses makes them prone to failure. That might be lots and lots of intensive focusing activity, exerting unusual forces on the lens or MF ring while doing AF, lots of AF in an unusual orientation like straight-up or straight-down, use in dusty or condensing environments, electrostatic discharge to the SDM electrical contacts from wiping the lens with certain kinds of cloth in a low-humidity environment, or something else. That explanation does not absolve the lens maker from responsibility for the product's quality but may explain why some SDM users never have a problem while others have nothing but problems.
07-05-2017, 08:35 AM   #12
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I have never endorsed the theory. I just asked what other theory fit the observation.
I find it odd that AF works fine if you turn on the camera (with the lens on). Wait 1-2 minutes before use. If you start using it immediately after turning the camera on, nothing happens.....
07-05-2017, 08:40 AM   #13
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I'm afraid an exact answer to your question might not be found out even by trained engineers, with your lens at hand to study and all the fancy equipment. Stiction? Bad soldering somewhere? Affected by slight variation in power delivery, or heat? Moving the lens' focus ring while waiting? Coincidence? Someone more knowledgeable than me might easily give you a dozen possible explanations, while missing the actual cause. Or not.
What I can tell you with 100% certainty is that it's not a huge capacitor needing to be charged.
07-05-2017, 08:42 AM   #14
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QuoteOriginally posted by Pål Jensen Quote
Then what is the explanation for the fact that the camera must be on for a minute or two before SDM starts to work?
From my limited research and personal experience with DA*16-50 (which wakes up in about 2 mins after several focus attempts in that time) and DA*50-135 (which takes up to 5 or 10 minutes even of course attempting focus during all this time) it seems the motor has some gunky lubricant or a lubricant that needs warmth around it to become more viscous and let the motor operate. I say this because repeated focusing attempts probably causes the motor to heat up a little causing the lubricant to loosen up or become viscous, if you will. And once that happens it functions normally until it is cold and lubricant loses its viscosity again.
I also observed that during the winter season this behavior is more pronounced. In very hot weather the wake up times are lesser or the lens wakes up almost instantly after a few focus attempts.

So the SDM issues (or the lubricant there in) are real. The motor by itself isn't an issue I think. It is either the lubricant and tight tolerances or an over torqued fitment of that motor on the body. Some people have claimed to have had success by twisting the screw (a small philips head) on the motor's shaft a few times. Probably losens a little bit and when that happened It worked without any wake up time. So I think it was/is the over torque or lubricant issue. Usually the motor is stuck on something and cannot move and hence eventually fails due to the blockages (either by bad lubricant or over torqued screw which when a bit loosened lets the motor works freely).

My lenses are out of warranty and I am going to give it a shot at some point. But I fear losing the weather sealing. So am still on the fence. I might let it fail and then convert it to screw drive when that happens as plan B.
07-05-2017, 08:43 AM   #15
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QuoteOriginally posted by photoptimist Quote
I'd suspect:
1) differential thermal expansion of the piezo elements and rotor
2) mechanical release of stiction from the forces induced by trying to get the lens to work
Neither is very convincing.
1) I cant see that there would be thermal changes from just mounting a lens and wait a couple of minutes.
2) I can't see how waiting a couple of minutes extra before you try to get the lens to work would make any difference in regards to stiction forces. If it needs some attempts before mechanically loosing up, it shuold be irrelevant how long time after you power on the camera you press the AF button.....

BTW I don't need to attempt AF so that the motor "warms up". All thats needed is to have the body turned on a few minutes before use.
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