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07-27-2015, 06:27 AM - 6 Likes   #1
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Found a cheap and effective way to fix SDM failures.

Hey guys, I found another cheap way to quick fix the SDM problem. You just hold the AF button down for a couple of seconds and let go, then you hold the AF button down for a couple of seconds and let go, repeat, repeat, and repeat until it starts to move and focus again.


Last edited by BigMackCam; 11-08-2017 at 10:05 AM. Reason: Edited at member's request
07-27-2015, 06:46 AM   #2
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That's... interesting... almost like you are recharging the motor or something Hope mine never fail but I'll have to remember this when it does.
07-27-2015, 06:53 AM   #3
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I don't have a SDM lens, but from reading this and a couple other threads, I wonder if the problem is with lubrication of the lens.


I don't know how these lenses are built but if there is a grease or oil used to lubricate the lens, it might be getting to sticky for the motor to turn the focus ring. When you activate the motor and start turning the focus ring, the friction is moving the grease around making it more pliable again so the motor works again.
07-27-2015, 07:00 AM   #4
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QuoteOriginally posted by bigdavephoto Quote
I don't have a SDM lens, but from reading this and a couple other threads, I wonder if the problem is with lubrication of the lens.


I don't know how these lenses are built but if there is a grease or oil used to lubricate the lens, it might be getting to sticky for the motor to turn the focus ring. When you activate the motor and start turning the focus ring, the friction is moving the grease around making it more pliable again so the motor works again.
This would conform to the observations that SDM lenses seem to act up more often when not used often. When this was a hot topic people often reported that the avoided problems by taking their lenses out every week or so to give them a work out. I suspect there is more involved but a lubrication problem might be part of it. I had a 50-135 which I bought very cheaply because the original owner thought the SDM was dead. It worked most of the time but would occasionally respond slowly or not at all. It was mild enough that I used it for more than a year before I had the SDM fixed by CRIS. I used that lens fairly often so I do not think lubrication distribution was a likely cause of the problem. We will probably never know but thanks to the OP for sharing a possible work around.

07-27-2015, 07:49 AM - 1 Like   #5
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I suspect you may have just raised the sale value of all the "dead" SDM lenses, for which I am sure many current owners will be thankful.
07-27-2015, 08:28 AM   #6
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I don't think you can give definitive advice on the basis of a single success. There have been many lenses that came back from school failure with other focusing ring manual manipulation techniques. And many that failed to respond. This is another good trick to try however.
07-27-2015, 08:45 AM   #7
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Or just convert it to screw drive mode and enjoy faster focusing
07-27-2015, 09:59 AM   #8
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QuoteOriginally posted by UncleVanya Quote
I don't think you can give definitive advice on the basis of a single success. There have been many lenses that came back from school failure with other focusing ring manual manipulation techniques. And many that failed to respond. This is another good trick to try however.
My single success, that worked for the 16-50 and 50-135, similar to as the OP describes but without leaving the lens cap on or using the green light. I just held the AF button and worked the focus ring back and forth and both came back to life. With my 300 this method did not work but what did work was turning the screwdrive mechanism on the mount with a small screwdriver and it has worked flawlessly since. I have since left the 16-50 and 50-135 converted to screwdrive since they seem to perform better/faster. I converted the 300 to screwdrive, just to test it out, but I preferred the SDM AF (screwdrive is loud on this lens and AF speed doesn't seem to improve) on that lens better so I switched back to SDM.

07-27-2015, 10:24 AM   #9
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QuoteOriginally posted by transam879 Quote
My single success, that worked for the 16-50 and 50-135, similar to as the OP describes but without leaving the lens cap on or using the green light. I just held the AF button and worked the focus ring back and forth and both came back to life. With my 300 this method did not work but what did work was turning the screwdrive mechanism on the mount with a small screwdriver and it has worked flawlessly since. I have since left the 16-50 and 50-135 converted to screwdrive since they seem to perform better/faster. I converted the 300 to screwdrive, just to test it out, but I preferred the SDM AF (screwdrive is loud on this lens and AF speed doesn't seem to improve) on that lens better so I switched back to SDM.
How does one make the lenses into using screwdrive?
07-27-2015, 11:03 AM   #10
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QuoteOriginally posted by LeDave Quote
How does one make the lenses into using screwdrive?
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/208353-how-...m-f-2-8-a.html
07-27-2015, 02:56 PM   #11
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I would say 80% of the failed SDM on Pentax lenses is due to the quick shift clutch mechanism getting gummed up. When the motor turns it hasn't got enough power to turn the focus mechanism inside the lens plus the focusing ring,which in turn does not let the lens focus,but you can do it manually because the quick shift clutch is engaged. The procedure described in this thread only proves that that is exactly what is being remedied,a sticky clutch.

Last edited by BCtoad; 07-27-2015 at 03:18 PM.
07-27-2015, 05:31 PM   #12
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QuoteOriginally posted by transam879 Quote
My single success, that worked for the 16-50 and 50-135, similar to as the OP describes but without leaving the lens cap on or using the green light. I just held the AF button and worked the focus ring back and forth and both came back to life. With my 300 this method did not work but what did work was turning the screwdrive mechanism on the mount with a small screwdriver and it has worked flawlessly since. I have since left the 16-50 and 50-135 converted to screwdrive since they seem to perform better/faster. I converted the 300 to screwdrive, just to test it out, but I preferred the SDM AF (screwdrive is loud on this lens and AF speed doesn't seem to improve) on that lens better so I switched back to SDM.
The reason why I stated it so that you constantly push the AF button after the green light turns off, is because when the green light turns off, it means it stopped focusing. So you want the lens to stay in focus while you spin the AF on the lens back and forth. I had it so that you have the lens caps on is so that it is dark enough to trick the camera into activating the green AF light. Although your way is also the same concept, just without the easy reminders of the AF light.
07-27-2015, 05:59 PM   #13
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I'll save a link to this thread--just in case!
07-28-2015, 05:48 AM   #14
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If the theory is that it is just the clutch, then it should not work on the 17-70, with no quick shift clutch or screw drive. Mine only has issues above 55mm, so that is likely to be a different issue altogether. Some others have had the SDM fail entirely.
09-06-2015, 01:05 AM   #15
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SDM on DA*300 not working

QuoteOriginally posted by LeDave Quote
Hey guys, It's me who've created the SDM Petition a few years back, but Pentax has not opened up to it even after over 1,000 signings. Well I've known how to fix SDM failures for awhile now. Here is how I fix it.

So you put your SDM lens on and you find it not auto focusing anymore. What you do is, you set the lens and camera to auto focus. Then with the lens cap still on, you hold down the AF button and with while the green AF light is lit up, you spin the auto focus ring on the lens 360 degrees to the left then 360 to the right in moderate to fast successions until the green light turns off. Then let go of the auto focus button or half-way shutter button (However you AF). Then you repeat, let me say again - Hold down the AF button and while the green AF light is lit up, spin the auto focus ring of the lens back and forth 360 degrees left to right, in moderate successions until the green light turns off. Then you repeat.

Keep doing this over and over and over until the lens comes back to life.

Hope this helps! Cheers.

With the DA* 16-50 I've had for about 4 years now. It has failed 3 times, I have been able to revive it with this method and now it still works fine after fixing it several months ago. My DA* 50-135, which is as old as my 16-50, has never seen failure (Thank God for that).

If this helped anyone and are able to create a video tutorial, feel free to do so.
Hi, I have tried to apply what you have suggested to my DA*300 as the SDM has suddenly stopped working. How long do you have to spin the focus back and forth before the blinking green light goes off? Not managed to get mine to go off yet.

Paul
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