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01-09-2011, 06:21 PM   #46
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QuoteOriginally posted by Hound Tooth Quote
Actually in a way I did. About 6 months after I bought my 50-135mm, when the apologists who convinced me to buy this lens in the first place started suffering SDM failures of their own, that's when I started to wonder if I'd made a mistake. Those apologists turned into realists. I started advocating against SDM at that time (long before my own failed). My own fears got confirmed just a few months later.

Like I said: history repeats itself over and over again. It's inevitable, any 50-135mm will fail within a short time span. Doesn't matter if it's 1 month or 3 years. And the repaired copy will fail too, within that same span.
Of course, there is a failure rate, but you just made those numbers up. I doubt the failure rate is higher than 10 percent at 5 years, but just as you did, I made up a number too.

01-09-2011, 06:47 PM   #47
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The problem is that no one except Pentax knows what the numbers are, so we're just guessing. Someone could try to do a proper survey, but it's not simple to do it correctly (eliminate bias) and get sufficient statistics etc.
01-09-2011, 08:34 PM   #48
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QuoteOriginally posted by Rondec Quote
Of course, there is a failure rate, but you just made those numbers up. I doubt the failure rate is higher than 10 percent at 5 years, but just as you did, I made up a number too.
No I didn't. Those numbers are based on reported failures (once again, known facts, not made up guessing).

Also, they're based on the fact that the 50-135mm is inherently flawed in its focus mechanism design. Imagine a weather resistant lens that can't focus, manually or automatically, when it gets to 32f. Whenever the lens gets too cold (and 32f isn't all that cold), the mechanism becomes so stiff that the clutch can no longer turn the focus mechanism. The focus ring just free-wheels and the focus group stays stuck. This happens after just a few months of using the lens. The clutch loses friction quickly with age. Especially if you frequently turn the focus ring past its limit, which happens very easily since there's no limit to how far you can turn it.

Now imagine how much effort the SDM motor needs to exert to overcome this resistance when the lens is cold. It's really no wonder they fail so often.

Anyone can try this for themselves, stick one in the freezer. Most household freezers are set to about 28f, give or take. This is warmer than Pentax weather resistant bodies are certified for. It's warmer than it is outside right now over here. Then see if the focus ring works anymore. If the lens is brand new, it might work fine. If it's a few months or years old, I bet the focus ring no longer works until the lens warms up again.

Last edited by Hound Tooth; 01-09-2011 at 10:54 PM.
01-09-2011, 09:07 PM   #49
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Is this specific to the 50-135 since it internally focuses, versus the extending 16-50 and 60-250?

01-09-2011, 09:27 PM   #50
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I purchased the DA 17-70 in mid-2010, used, from the Marketplace here. No issues so far. I don't know the original purchase date. I do expect that it will fail somehow, at some point in time. SDM lenses are precision, electro-mechanical devices and these will fail in some way, and I considered this when I bought it. So the question becomes how long is expected life, and how much does the insurance cost? Glenn
01-09-2011, 09:56 PM - 1 Like   #51
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QuoteOriginally posted by Loren E Quote
Is this specific to the 50-135 since it internally focuses, versus the extending 16-50 and 60-250?
I think this particular flaw is specific to the 50-135mm, but I don't know because I've never used any other SDM lenses. When you turn the focus ring on the 50-135mm, once you reach either limit (close focus or infinity), you can continue to turn the focus ring past that limit. The mechanism makes a "clunk" sound as you reach the limit, but the ring can keep turning, albeit with a small amount of added resistance. Doing this means you're turning against the internal clutch, which wears out that clutch over time. Eventually, the clutch no longer provides enough friction to turn the focus mechanism, especially as the lens is used in colder temperatures.

None of this explains the SDM failure of course. I think the clutch wearing out is another symptom of the underlying problem. The focus mechanism requires too much force to operate. So the SDM motor is overworked most of the time, especially when the lens is cold. I saw the first symptoms of failure at temperatures of 40f, about 9 months after I bought the lens. When temperatures warmed up, the SDM motor started acting "normally" again.

Another thing that anyone can try: the screw-drive mechanism. If you try to turn the screw-drive by hand, you'll find that it takes 17 turns to go from infinity to close focus. SEVENTEEN!!! Most Pentax lenses need 3 to 7 turns at most. Some macro lenses need 10 turns. It seems the Pentax engineers were aware of the fact that the focus mechanism requires excessive force to move, and so they down-geared it excessively to reduce the required torque. But I guess they didn't down-gear it enough, because the SDM motor still gets overwhelmed by it.

(this would also explain why the 50-135mm is one of the slowest-focusing lenses in the Pentax lineup)
01-10-2011, 04:48 AM   #52
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QuoteOriginally posted by Hound Tooth Quote
No I didn't. Those numbers are based on reported failures (once again, known facts, not made up guessing).

Also, they're based on the fact that the 50-135mm is inherently flawed in its focus mechanism design. Imagine a weather resistant lens that can't focus, manually or automatically, when it gets to 32f. Whenever the lens gets too cold (and 32f isn't all that cold), the mechanism becomes so stiff that the clutch can no longer turn the focus mechanism. The focus ring just free-wheels and the focus group stays stuck. This happens after just a few months of using the lens. The clutch loses friction quickly with age. Especially if you frequently turn the focus ring past its limit, which happens very easily since there's no limit to how far you can turn it.

Now imagine how much effort the SDM motor needs to exert to overcome this resistance when the lens is cold. It's really no wonder they fail so often.

Anyone can try this for themselves, stick one in the freezer. Most household freezers are set to about 28f, give or take. This is warmer than Pentax weather resistant bodies are certified for. It's warmer than it is outside right now over here. Then see if the focus ring works anymore. If the lens is brand new, it might work fine. If it's a few months or years old, I bet the focus ring no longer works until the lens warms up again.
The "numbers" are not based on number of lenses sold versus number serviced. They are based on number of complaints. That is completely different.

I shot two weeks ago with my 50-135 at -10F. It is two years old and had no issues at all with focusing. I hate anecdotal evidence in either direction, but since it is impossible to bring scientific method to bear on this, I guess I'll just talk about my lens...
01-10-2011, 12:28 PM   #53
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I am one of those blissful owners of the 50-135. I am NOT an apologist and i dont make RANDOM guesses, as you state, Houndstooth.

My lens is taking good photos and has for at least 2 years.

I think this nothing but a rant by a disgruntled Pentax owner.

Why don't you just sell up, houndstooth, and go spend your receipts PLUS a lot more on a Nikon or Canon outfit.

I am happy and I know many are. If my lens fails, and I find your statement "it WILL" very presumptuous, then so be it, I will get it repaired or replaced with something else.

I am not denying there have been failures, and successes. How many?? Who cares.

I say, at times, cars fail, computers fail, microwave ovens fail, etc etc. And so does all brands of Photographic equipment
So instead of sitting here picking the eyes out of everything Pentax, why dont people get out there and take photos.
Pentax will do me and always has.

01-10-2011, 07:01 PM   #54
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bahaha! There's no more ardent a supporter than one who chose to spend a boat load of money on a product. Especially when anyone else DARES to disagree on the greatness of said product.

But to recommend that others make the same investment based on their own limited experience while disregarding the mountains of evidence is a disservice. Letting Pentax off the hook for never owning up to this problem is shameful.

QuoteOriginally posted by Bramela Quote
I say, at times, cars fail, computers fail, microwave ovens fail, etc etc. And so does all brands of Photographic equipment.
Precisely. And how a company deals with such failure is what defines them in the eyes of its customers. Pentax has done nothing about this. While lenses fail repeatedly, while customers are stuck paying hundreds of dollars to get a flawed product repaired over and over again, Pentax sits on its hands and essentially tells the world "Not me mate!"

You people make it worse.
01-10-2011, 07:19 PM   #55
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QuoteOriginally posted by Bramela Quote
I am one of those blissful owners of the 50-135...

My lens is taking good photos and has for at least 2 years.

I think this nothing but a rant by a disgruntled Pentax owner.
How does it feel to own a ticking time bomb? You KNOW it's merely a matter of time, right? Then you too will join the "disgruntled" masses. Until then enjoy your 50-135, however with a little luck you could sell before it poops out.
01-10-2011, 07:31 PM   #56
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Why are only the people with complaints to be taken seriously and those happy with a product are not? Doesn't make sense to me. Those with complaints are always louder and therefore tend to skew the noise in that direction on the internet, but that doesn't mean that they really know anything about the number of failures out there.
01-10-2011, 11:23 PM   #57
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"A ticking timebomb??,"

This has to be turning into nothing but a big joke.

I am out of it here and now.
01-11-2011, 12:06 AM   #58
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QuoteOriginally posted by Rondec Quote
Why are only the people with complaints to be taken seriously and those happy with a product are not? Doesn't make sense to me. Those with complaints are always louder and therefore tend to skew the noise in that direction on the internet, but that doesn't mean that they really know anything about the number of failures out there.
I don't see where anybody is taking one group more seriously than the other. I think everybody is taking themselves more seriously than everybody else. Probably just human nature or some such thing, since we have no way of knowing how credible the other person is.

Those who have experienced a failure do have one advantage though; they know exactly how long their lens lasted. So they are able to bring at least one hard fact to the table. Those whose lenses have not failed have no way of knowing how long they will last. Their lens could keep going for years, or could fail tomorrow. You just don't know, so any assertions are only speculation. The "disgruntleds", however, KNOW exactly how long their lens was good for.
01-11-2011, 05:21 AM   #59
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QuoteOriginally posted by Edgar_in_Indy Quote
I don't see where anybody is taking one group more seriously than the other. I think everybody is taking themselves more seriously than everybody else. Probably just human nature or some such thing, since we have no way of knowing how credible the other person is.

Those who have experienced a failure do have one advantage though; they know exactly how long their lens lasted. So they are able to bring at least one hard fact to the table. Those whose lenses have not failed have no way of knowing how long they will last. Their lens could keep going for years, or could fail tomorrow. You just don't know, so any assertions are only speculation. The "disgruntleds", however, KNOW exactly how long their lens was good for.
But, I live in both camps. I have had a lens (the 16-50) in which the SDM motor crapped out after about six months of use. I have had it repaired under warranty and have had no further problems with it (18 months of further useage). I also have the DA 50-135 which is over two years old and has had no issues.

I really don't live in constant fear, like some have suggested and I recently bought a new lens (the DA *55) and did not consider the SDM as an issue -- neither positive nor negative. If someday the lenses need to be serviced, then I will get them serviced. I use them heavily and it is expected that that will happen one day. I am pleased with them optically and that is what counts in the long run to me.
01-11-2011, 05:28 AM   #60
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The problem with SDM products is you never know what the final cost of ownership will be. If they came with a 5 year warranty, I'd be inclined to give the 50-135 and the 60-250 a go, but now as it stands, I much prefer third party options... and there are some very good ones... and they all offer more peace of mind and value than Pentax products.
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