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10-12-2018, 07:27 PM   #1
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Used 50-135 F/2.8 SMC DA * ed if sdm from 2008

As the title suggest, I found a used 50-135 F/2.8 SMC DA * ed if sdm. The guy bought it in 2008 and switched to Nikon in 2013, so it hasn't been used since. He says its still works and optically and cosmetically its in great shape. But I've read to many horror stories about the sdm failing that I'm nervous to buy it even though its selling for 200. So I was wondering, If I buy it and it does fail, am I guarenteed to be able to convert it to screw drive (I shoot with with a k50, not sure if it matters)

10-12-2018, 07:45 PM   #2
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The secret is to always exercise the SDM auto focus motor every few days. I understand the problem is the lubricants used in the quick shift mechanism. If you don't use the lens then the lubricants harden to such an extent that the SDM motor can bot turn the auto focus in the lens.

And yes, it is possible to convert this lens to screw drive only. There is a regular listing in the Marketplace for this service.

$200 seems like a very good price.

Regards

Chris
10-12-2018, 08:25 PM   #3
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QuoteOriginally posted by seventhdr Quote
The secret is to always exercise the SDM auto focus motor every few days. I understand the problem is the lubricants used in the quick shift mechanism. If you don't use the lens then the lubricants harden to such an extent that the SDM motor can bot turn the auto focus in the lens.

And yes, it is possible to convert this lens to screw drive only. There is a regular listing in the Marketplace for this service.

$200 seems like a very good price.

Regards

Chris
If it hasn't been used in 5 years, but works when I purchase it it works, is it safe to assume the SDM isn't damaged as of yet?
And if I convert it its guaranteed to work?
And k-50 can use the screw drive?
Thank you so much seventhdr

---------- Post added 10-12-18 at 09:31 PM ----------

QuoteOriginally posted by seventhdr Quote
The secret is to always exercise the SDM auto focus motor every few days. I understand the problem is the lubricants used in the quick shift mechanism. If you don't use the lens then the lubricants harden to such an extent that the SDM motor can bot turn the auto focus in the lens.

And yes, it is possible to convert this lens to screw drive only. There is a regular listing in the Marketplace for this service.

$200 seems like a very good price.

Regards

Chris
I guess my real question is, if I buy it and the motor fails, am I almost guaranteed to still have a usable lens? I really want the lens but 200 is still a bit of money for me.
Nathan
10-12-2018, 10:02 PM   #4
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Two hundred bucks? Just buy it! Brilliant lens.

If the SDM fails, converting it to screw drive yourself is not terribly difficult, or if you'd rather leave it to @UncleVanya it won't cost you much.

10-12-2018, 11:04 PM   #5
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QuoteOriginally posted by Sandy Hancock Quote
Two hundred bucks? Just buy it! Brilliant lens.

If the SDM fails, converting it to screw drive yourself is not terribly difficult, or if you'd rather leave it to @UncleVanya it won't cost you much.
So theres no chance the lens will be completely unusable?
10-12-2018, 11:07 PM   #6
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QuoteOriginally posted by Sandy Hancock Quote
Two hundred bucks? Just buy it! Brilliant lens.

If the SDM fails, converting it to screw drive yourself is not terribly difficult, or if you'd rather leave it to @UncleVanya it won't cost you much.
I agree- a fantastic price for a fantastic lens! I've had mine put away for many months on end, and when I get it out it still works fine. I've also had mine since 2008. I don't leave it on a camera body, however, just stored in its cloth case, or in a belt holster case in a cabinet. From what I've read here, the conversion to screw-driven is no big deal if needed. I don't use it all the time, but it is one of my favorite lenses. Oddly, I find myself using it more after getting the KP.
10-13-2018, 05:35 AM   #7
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QuoteOriginally posted by nmcleod1993 Quote
So theres no chance the lens will be completely unusable?
As long as it focuses manually and registers on the camera and allows aperture control it will work well. Most likely you can get it to work in screw drive mode if those two things are true. Even if you can't it is a good enough lens that $200 for manual focus wouldn't be irrational.

---------- Post added 10-13-18 at 08:36 AM ----------

Conversion to screw drive isn't terribly difficult but does require an older body.

10-13-2018, 08:46 AM   #8
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Is it ok if it turns the manual ring while focusing with AF?

QuoteOriginally posted by UncleVanya Quote
As long as it focuses manually and registers on the camera and allows aperture control it will work well. Most likely you can get it to work in screw drive mode if those two things are true. Even if you can't it is a good enough lens that $200 for manual focus wouldn't be irrational.

---------- Post added 10-13-18 at 08:36 AM ----------

Conversion to screw drive isn't terribly difficult but does require an older body.
10-13-2018, 11:53 AM   #9
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$200 is a great price. I can’t see how you can pass on it. As said if you can only focus manually it is still a great deal. I’d be willing to buy it to either resell this or sell my current copy depending on condition
10-13-2018, 04:53 PM   #10
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QuoteOriginally posted by nmcleod1993 Quote
Is it ok if it turns the manual ring while focusing with AF?
I don't remember my manual focus ring turning by itself during af. If thats what you mean I don't think that is normal. If you mean you can freely turn the ring during af manually then that is ok and by design. It is part of how quickshift works on that lens.
10-13-2018, 08:53 PM   #11
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QuoteOriginally posted by seventhdr Quote
The secret is to always exercise the SDM auto focus motor every few days. I understand the problem is the lubricants used in the quick shift mechanism. If you don't use the lens then the lubricants harden to such an extent that the SDM motor can bot turn the auto focus in the lens.
This "secret" seems like a PITA, especially if it isn't a lens you use all the time naturally.
10-14-2018, 06:06 AM   #12
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QuoteOriginally posted by leekil Quote
This "secret" seems like a PITA, especially if it isn't a lens you use all the time naturally.
Take it with a grain of salt since it's the result of anecdotal experiences. Well meaning, but not at all scientific. FWIW, I've done everything "wrong" according to this secret, yet my lenses work fine. I recently bought a used 50-135 for more than double the OP's deal. It's a great lens, but like any used lens, things can go wrong.
10-14-2018, 07:35 AM - 1 Like   #13
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QuoteOriginally posted by rogerstg Quote
Take it with a grain of salt since it's the result of anecdotal experiences. Well meaning, but not at all scientific. FWIW, I've done everything "wrong" according to this secret, yet my lenses work fine. I recently bought a used 50-135 for more than double the OP's deal. It's a great lens, but like any used lens, things can go wrong.
100% agree on the secret... These lenses sit on shelves in boxes and don't have freshness dates; camera stores don't take them out and wake them up. I think the symptom - failing sdm losing torque - may drive the behavior. Stiction (increased static friction) could potentially increase while a lens is stored making the startup harder for a failing motor. Sometimes the failing sdm motor might struggle to get things moving. The capacitor explanation however seems like magical thinking. For lenses without failing sdm I don't recommend this as the practice appears to me to be unnecessary.
10-14-2018, 03:29 PM   #14
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QuoteOriginally posted by leekil Quote
This "secret" seems like a PITA, especially if it isn't a lens you use all the time naturally.
Yes. You're right. It is a pain in the arse. But it's a great lens.

By exercising the lens you avoid an SDM failure due to poor engineering design by Pentax. Pentax should really have been more forward to buyers about acknowledging the problem, retrofitting failed lenses and engineering an improvement to the components used in the lenses that contributed to the problem. It's a typical Japanese thing though to not admit to your failures.

Regards

Chris
10-15-2018, 08:55 AM - 2 Likes   #15
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Got the lens, no SDM failure yet. But boy is it a fun lens. Thanks all for the advice and help I really appreciate it
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