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04-10-2016, 09:36 AM   #1
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SDM failure or what?

I periodically run my SDM lenses to 'exercise' them, and everything has been fine...until today!

I put my 50-135 on my K5II, and it wouldn't focus! My 17-70 and 300 would, as did my new DC 16-85.

Oh ********! I thought. Classic SDM failure, but...

With nothing to lose I tried the 50-135 again. Worked! Then I noticed that it would focus from far to near, but not near to far.

Odd!

Tried the 50-135 on my KS1 and K20D. Focussed first time, every time, far to near, near to far, continuous AF - all perfect!

Must be contacts. Cleaned them on the body and lens (wiped with paper hanky) .

Tried lens again. No difference. Still not playing nicely. Tried other SDM lenses on K5II - perfect.

So, whilst it seems like the answer is 'SDM', I've never read anything that describes symptoms like mine.

To recap, the lens will focus perfectly on two out of three bodies, but only far to near on my K5II. All other SDM and DC lenses operate perfectly on the K5II.

Suggestions anyone please?

04-10-2016, 03:11 PM   #2
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QuoteOriginally posted by JohnX Quote
I periodically run my SDM lenses to 'exercise' them, and everything has been fine...until today!

I put my 50-135 on my K5II, and it wouldn't focus! My 17-70 and 300 would, as did my new DC 16-85.

Oh ********! I thought. Classic SDM failure, but...

With nothing to lose I tried the 50-135 again. Worked! Then I noticed that it would focus from far to near, but not near to far.

Odd!

Tried the 50-135 on my KS1 and K20D. Focussed first time, every time, far to near, near to far, continuous AF - all perfect!

Must be contacts. Cleaned them on the body and lens (wiped with paper hanky) .

Tried lens again. No difference. Still not playing nicely. Tried other SDM lenses on K5II - perfect.

So, whilst it seems like the answer is 'SDM', I've never read anything that describes symptoms like mine.

To recap, the lens will focus perfectly on two out of three bodies, but only far to near on my K5II. All other SDM and DC lenses operate perfectly on the K5II.

Suggestions anyone please?
I exercise my DA 17 -70 at least weekly and my DA* 200 at least monthly. In addition when I turn the camera on with either of these lenses on I give it about a minute or two for the capacitor in the lens to charge before focusing on something. This seems to keep them working reliably. Several times before I started doing this, I had given them up for dead. and had similar experiences as yours with my two SDM lenses.
04-10-2016, 04:02 PM   #3
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QuoteOriginally posted by JohnX Quote
I periodically run my SDM lenses to 'exercise' them, and everything has been fine...until today!

I put my 50-135 on my K5II, and it wouldn't focus! My 17-70 and 300 would, as did my new DC 16-85.

Oh ********! I thought. Classic SDM failure, but...

With nothing to lose I tried the 50-135 again. Worked! Then I noticed that it would focus from far to near, but not near to far.

Odd!

Tried the 50-135 on my KS1 and K20D. Focussed first time, every time, far to near, near to far, continuous AF - all perfect!

Must be contacts. Cleaned them on the body and lens (wiped with paper hanky) .

Tried lens again. No difference. Still not playing nicely. Tried other SDM lenses on K5II - perfect.

So, whilst it seems like the answer is 'SDM', I've never read anything that describes symptoms like mine.

To recap, the lens will focus perfectly on two out of three bodies, but only far to near on my K5II. All other SDM and DC lenses operate perfectly on the K5II.

Suggestions anyone please?
Have you noticed what was our battery status on the K5II? Sometimes with battery close to depletion you might run into similar problem. Charge the battery fully and try again, would be my suggestion.
04-10-2016, 11:28 PM   #4
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Thanks guys. I've tried your suggestions, with no luck, but have got the lens going again by manually operating the screw drive up and down a few times.

Despite the fact that a change of battery didn't immediately help, I wonder if power is part of the problem? There has to be a fundamental difference between the three camera bodies, and the power each delivers to the attached lens might be the answer.

The 50-135 has always been slow to track compared to other lenses. I understand the 16-50 is too, but have no personal experience. This infers mechanical 'drag' which needs to be overcome. Conversely the 17-70 is zippy by comparison.

To overcome this drag the camera body has to deliver power. Could it be different model to model? If so, could many SDM 'failures' be attributable to power 'bus' issues not the SDM itself?

The lens is now operating normally, which good this model is slooowly!


Last edited by JohnX; 04-10-2016 at 11:35 PM.
04-11-2016, 06:57 AM   #5
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QuoteOriginally posted by JohnX Quote
To overcome this drag the camera body has to deliver power. Could it be different model to model? If so, could many SDM 'failures' be attributable to power 'bus' issues not the SDM itself?
I would tender this answer: I don't think so.

Since I convert SDM to ScrewDrive I have seen quite a few of these failed SDM lenses. I have two SDM enabled bodies - a K100D Super and a K3. I test all failed SDM lenses on those and a K100D (screw drive only) body to ensure that SDM is dead and ScrewDrive works before converting. To date NONE have "woken up" and worked. This may be due to the fact that these are typically lenses that have been dead for a while and their owners have tried everything - but it does seem to shoot down the "bus" theory. My own SDM lenses all work great with my bodies.
04-12-2016, 02:02 AM   #6
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Thanks UncleVanya.

As you've worked on faulty SDM lenses, especially the 50-135, can you tell me what happens to the screwdrive mechanism when the lenses is focussed using SDM? As fast as I can tell the two focussing methods are independent, which can't be right, can it?
04-12-2016, 05:10 AM   #7
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QuoteOriginally posted by JohnX Quote
Thanks UncleVanya.

As you've worked on faulty SDM lenses, especially the 50-135, can you tell me what happens to the screwdrive mechanism when the lenses is focussed using SDM? As fast as I can tell the two focussing methods are independent, which can't be right, can it?
I'm not sure I follow the question entirely. I believe the two are separated by a clutch system that permits the two systems to decouple.
04-12-2016, 11:50 AM   #8
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For info and reference maybe, on the 'other' forum, a user has posted some nice pix of the SDM focus motor assembly, as removed from his DA*300 after repairs:
Post Office delivered my repaired lens today (SDMotor photos attached): Pentax SLR Talk Forum: Digital Photography Review

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