Conversion to screwdrive seems to have fixed SDM (?)

dlhawes · 07-05-2021, 05:38 AM - **1 Like**

Originally posted by clickclick

I just want to be sure I'm interpreting this correctly. You were just using this as a method to spin the ring quickly for a long period versus turning it by hand? ...

Never mind all that, it turned out not to be an effective solution over time.

Last edited by dlhawes; 07-13-2021 at 09:05 AM.

**clickclick** · 07-05-2021, 07:28 AM

Originally posted by dlhawes

Correct. Did it one way and then the other at probably around .... I was thinking I'd estimate the RPM's, but then the sanding drum is about 1.125" in diameter, and the focus ring is about two and a half inches, so there's a gearing effect - the drum is spinning much, much faster than the focus ring, so which do I estimate? Put it this way, it was movin' right quick!

It may have been overkill, but the thing works.

Thanks. I'll keep this trick in my back pocket if I get desperate. I probably need to go take some shots with the critter. It's been sitting a bit now, and I bet it's jealous again.

**Apet-Sure** · 07-05-2021, 11:19 AM - **1 Like**

Originally posted by dlhawes

I was thinking I'd estimate the RPM's, but then the sanding drum is about 1.125" in diameter, and the focus ring is about two and a half inches, so there's a gearing effect

So, I couldn't resist nerding out for a moment. I had an engineering job where we worked with gearing a fair amount. Take the diameter of the drive wheel (sanding drum) and divide it by the diameter of the driven wheel (focus ring), then multiply the result by the RPM of the drive motor (drill). 1.125" ÷ 2.5" = 0.45. If the drill was spinning at 100rpm, the focus ring was spinning at 45rpm. If you don't know the drill's rpm, use the TLAR method of arriving at engineering solutions - That Looks About Right.

artrasa · 07-05-2021, 02:09 PM - **1 Like**

It's great that you managed to get your lens mostly working again. I'm happy for you.

But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this, and many others, threads about malfunctioning SDM motors. Is it really such a widespread problem?

**UncleVanya** · 07-05-2021, 06:08 PM

Originally posted by artrasa

It's great that you managed to get your lens mostly working again. I'm happy for you.

But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this, and many others, threads about malfunctioning SDM motors. Is it really such a widespread problem?

That’s depends how you measure it. And when the lens was made. By the loudness of the vocal angry mobs on forums every sdm lens in the world is junk (lol). By survey of forum members I can’t recall the exact numbers but it wasn’t too high. But good real numbers are very hard to get.

As for when, the sdm motor systems were redesigned a couple of times. Those since the redesign seem less problematic. Sdm as a term is still used even with new designs but the newest sdm lenses seem pretty solid.

The fact that the first four (or five really) sdm / screwdrive compatible lenses were very premium lenses made the sting of failure worse. Additionally some people had multiple failures with the same lens while other users have never had a problem.

**clickclick** · 07-05-2021, 08:34 PM

I feel like the 16-50 is the one you really hear about. I also have the 50-135, which I purchased at the same time, and a 60-250 I picked up used, so some age on that, and then the 20-40 Limited, and it's only been the 16-50 that's given me fits. I don't think I've ever heard of the 20-40 having issues either.

**jatrax** · 07-06-2021, 07:58 AM

Originally posted by artrasa

But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this

Note that issues with the SDM mechanism have been limited to a now older range of lenses, primarily the DA*16-50, DA*50-135 and DA*60-250. New lenses like the DFA 24-70, 15-30 and 70-210 are listed as SDM but supposedly (almost certainly) use a different motor completely. It is unfortunate (IMHO) that Ricoh used the same terminology considering the poor reputation of the 'SDM' term.

But as UncleVanya states real numbers are hard to come by, and likely the actual failure percentage was not nearly as high as forum posts might indicate. I would have no hesitation in buying a new SDM lens, in fact I have all three of the DFA ones. However, buying a used DA* one I would be cautious. But of those lenses the two most commonly mentioned (possibly because they sold the most) are the 16-50 and the 50-135 both of which can be converted to screw-drive which in my experience actually works better and faster than the SDM in those lenses.

mtkeller · 07-06-2021, 08:25 PM

Originally posted by clickclick

I feel like the 16-50 is the one you really hear about. I also have the 50-135, which I purchased at the same time, and a 60-250 I picked up used, so some age on that, and then the 20-40 Limited, and it's only been the 16-50 that's given me fits. I don't think I've ever heard of the 20-40 having issues either.

20–40 Ltd has a DC focusing motor, not SDM.

**clickclick** · 07-07-2021, 07:11 PM - **1 Like**

Originally posted by mtkeller

20–40 Ltd has a DC focusing motor, not SDM.

Yep. Can't believe I forgot that. Thanks

**Apet-Sure** · 07-08-2021, 11:40 AM

60-250 SDM not responding again.

Oh well.

krazny · 07-08-2021, 12:14 PM

Originally posted by Apet-Sure

60-250 SDM not responding again.

Oh well.

Did you leave it on the camera or remove it in between?

troika · 07-08-2021, 12:56 PM

What's keeping Pentax from changing all of these to DC or PLM going forward? How hard would it be for them to offer a retro-fit?

There are so many great Pentax lenses that carry this serious liability. It's a shame.

**Apet-Sure** · 07-08-2021, 01:02 PM

Originally posted by krazny

Did you leave it on the camera or remove it in between?

It's been on the camera since my earlier posts above. After it started working again I exercised it every day. Then the last couple days - no response even though the battery showed fully charged. Today the battery needed recharging. Now with a full charge still no SDM life.

krazny · 07-08-2021, 01:18 PM

Did you need to give it a moment before it kicked into action or was it instantly?

For how long are you holding the shutter/focus button or how often do you hold it for some time?

**Apet-Sure** · 07-08-2021, 04:24 PM

Originally posted by krazny

Did you need to give it a moment before it kicked into action or was it instantly?For how long are you holding the shutter/focus button or how often do you hold it for some time?

After I had rotated the focus ring back and forth for many minutes, I tried viewfinder AF. Nothing. Switched to Live View and it worked instantly. Switched back to viewfinder AF and it worked instantly. Next day both viewfinder and Live View AF worked instantly. Yesterday and today both don't work after holding down back focus button for maybe 6-8 seconds on each attempt.

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07-05-2021, 05:38 AM - 1 Like	#16
dlhawes Guest	Originally posted by clickclick I just want to be sure I'm interpreting this correctly. You were just using this as a method to spin the ring quickly for a long period versus turning it by hand? ... Never mind all that, it turned out not to be an effective solution over time. Last edited by dlhawes; 07-13-2021 at 09:05 AM.

07-05-2021, 07:28 AM	#17
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,903	Originally posted by dlhawes Correct. Did it one way and then the other at probably around .... I was thinking I'd estimate the RPM's, but then the sanding drum is about 1.125" in diameter, and the focus ring is about two and a half inches, so there's a gearing effect - the drum is spinning much, much faster than the focus ring, so which do I estimate? Put it this way, it was movin' right quick! It may have been overkill, but the thing works. Thanks. I'll keep this trick in my back pocket if I get desperate. I probably need to go take some shots with the critter. It's been sitting a bit now, and I bet it's jealous again.

07-05-2021, 11:19 AM - 1 Like	#18
Apet-Sure Site Supporter Join Date: Dec 2015 Location: Goldsboro North Carolina Photos: Gallery \| Albums Posts: 2,861	Originally posted by dlhawes I was thinking I'd estimate the RPM's, but then the sanding drum is about 1.125" in diameter, and the focus ring is about two and a half inches, so there's a gearing effect So, I couldn't resist nerding out for a moment. I had an engineering job where we worked with gearing a fair amount. Take the diameter of the drive wheel (sanding drum) and divide it by the diameter of the driven wheel (focus ring), then multiply the result by the RPM of the drive motor (drill). 1.125" ÷ 2.5" = 0.45. If the drill was spinning at 100rpm, the focus ring was spinning at 45rpm. If you don't know the drill's rpm, use the TLAR method of arriving at engineering solutions - That Looks About Right.

07-05-2021, 02:09 PM - 1 Like	#19
artrasa Senior Member Join Date: May 2021 Photos: Gallery \| Albums Posts: 185	It's great that you managed to get your lens mostly working again. I'm happy for you. But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this, and many others, threads about malfunctioning SDM motors. Is it really such a widespread problem?

07-05-2021, 06:08 PM	#20
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,385	Originally posted by artrasa It's great that you managed to get your lens mostly working again. I'm happy for you. But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this, and many others, threads about malfunctioning SDM motors. Is it really such a widespread problem? That’s depends how you measure it. And when the lens was made. By the loudness of the vocal angry mobs on forums every sdm lens in the world is junk (lol). By survey of forum members I can’t recall the exact numbers but it wasn’t too high. But good real numbers are very hard to get. As for when, the sdm motor systems were redesigned a couple of times. Those since the redesign seem less problematic. Sdm as a term is still used even with new designs but the newest sdm lenses seem pretty solid. The fact that the first four (or five really) sdm / screwdrive compatible lenses were very premium lenses made the sting of failure worse. Additionally some people had multiple failures with the same lens while other users have never had a problem.

07-05-2021, 08:34 PM	#21
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,903	I feel like the 16-50 is the one you really hear about. I also have the 50-135, which I purchased at the same time, and a 60-250 I picked up used, so some age on that, and then the 20-40 Limited, and it's only been the 16-50 that's given me fits. I don't think I've ever heard of the 20-40 having issues either.

07-06-2021, 07:58 AM	#22
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by artrasa But I have to say that I would be a bit hesitant to spend money on lenses equipped with SDM focusing systems in future after reading this Note that issues with the SDM mechanism have been limited to a now older range of lenses, primarily the DA16-50, DA50-135 and DA60-250. New lenses like the DFA 24-70, 15-30 and 70-210 are listed as SDM but supposedly (almost certainly) use a different motor completely. It is unfortunate (IMHO) that Ricoh used the same terminology considering the poor reputation of the 'SDM' term. But as UncleVanya states real numbers are hard to come by, and likely the actual failure percentage was not nearly as high as forum posts might indicate. I would have no hesitation in buying a new SDM lens, in fact I have all three of the DFA ones. However, buying a used DA one I would be cautious. But of those lenses the two most commonly mentioned (possibly because they sold the most) are the 16-50 and the 50-135 both of which can be converted to screw-drive which in my experience actually works better and faster than the SDM in those lenses.

07-06-2021, 08:25 PM	#23
mtkeller Veteran Member Join Date: Feb 2019 Location: Sioux City, IA Photos: Gallery Posts: 938	Originally posted by clickclick I feel like the 16-50 is the one you really hear about. I also have the 50-135, which I purchased at the same time, and a 60-250 I picked up used, so some age on that, and then the 20-40 Limited, and it's only been the 16-50 that's given me fits. I don't think I've ever heard of the 20-40 having issues either. 20–40 Ltd has a DC focusing motor, not SDM.

07-07-2021, 07:11 PM - 1 Like	#24
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,903	Originally posted by mtkeller 20–40 Ltd has a DC focusing motor, not SDM. Yep. Can't believe I forgot that. Thanks

07-08-2021, 11:40 AM	#25
Apet-Sure Site Supporter Join Date: Dec 2015 Location: Goldsboro North Carolina Photos: Gallery \| Albums Posts: 2,861	60-250 SDM not responding again. Oh well.

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07-08-2021, 12:14 PM	#26
krazny Senior Member Join Date: Feb 2016 Posts: 118 Original Poster	Originally posted by Apet-Sure 60-250 SDM not responding again. Oh well. Did you leave it on the camera or remove it in between?

07-08-2021, 12:56 PM	#27
troika Pentaxian Join Date: Dec 2012 Location: Seattle, WA USA Posts: 1,753	What's keeping Pentax from changing all of these to DC or PLM going forward? How hard would it be for them to offer a retro-fit? There are so many great Pentax lenses that carry this serious liability. It's a shame.

07-08-2021, 01:02 PM	#28
Apet-Sure Site Supporter Join Date: Dec 2015 Location: Goldsboro North Carolina Photos: Gallery \| Albums Posts: 2,861	Originally posted by krazny Did you leave it on the camera or remove it in between? It's been on the camera since my earlier posts above. After it started working again I exercised it every day. Then the last couple days - no response even though the battery showed fully charged. Today the battery needed recharging. Now with a full charge still no SDM life.

07-08-2021, 01:18 PM	#29
krazny Senior Member Join Date: Feb 2016 Posts: 118 Original Poster	Did you need to give it a moment before it kicked into action or was it instantly? For how long are you holding the shutter/focus button or how often do you hold it for some time?

07-08-2021, 04:24 PM	#30
Apet-Sure Site Supporter Join Date: Dec 2015 Location: Goldsboro North Carolina Photos: Gallery \| Albums Posts: 2,861	Originally posted by krazny Did you need to give it a moment before it kicked into action or was it instantly?For how long are you holding the shutter/focus button or how often do you hold it for some time? After I had rotated the focus ring back and forth for many minutes, I tried viewfinder AF. Nothing. Switched to Live View and it worked instantly. Switched back to viewfinder AF and it worked instantly. Next day both viewfinder and Live View AF worked instantly. Yesterday and today both don't work after holding down back focus button for maybe 6-8 seconds on each attempt.