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05-09-2012, 04:28 AM   #1
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AF problem with DA 50-135mm on K20D

Hello,

I'm having a problem with my DA 50-135mm lens. It just doesn't auto-focus when i try to use it on my K20D. At first i thought it was a technical problem with the lens itself, but it worked smoothly on someone else's camera - unfortunately i didn't have the chance to learn which camera he used. I've been searching on the internet and asking colleagues about this for a long time. I couldn't find any related updates / firmware. Does anyone else have the same problem as i do? or what do you think causes the problem?

Thanks you for your help.

camera : Pentax K20D
lens : Pentax DA 50-135mm F2.8

05-09-2012, 04:54 AM   #2
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Have these two ever worked together ok?

Don't have the problem with my K20D/50-135, but try cleaning the contacts on the camera body and lens using a soft dry cloth in the first instance.
05-09-2012, 05:52 AM   #3
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cleared, but the result did not change :-)
05-09-2012, 06:02 AM   #4
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Does the firmware version currently installed allow operation of SDM lenses?

05-09-2012, 06:21 AM   #5
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Currently installed firmware1.04
05-10-2012, 09:57 AM   #6
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QuoteOriginally posted by JohnX Quote
Have these two ever worked together ok?

Don't have the problem with my K20D/50-135, but try cleaning the contacts on the camera body and lens using a soft dry cloth in the first instance.

and yes, at first they worked ok together just for a short while. then AF stopped working for no reason.
05-10-2012, 08:58 PM   #7
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Well, it's typical SDM behavior, so nothing new here.
05-10-2012, 11:32 PM   #8
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If the camera that it was tested on was a K100D or earlier model or a K10D with firmware before 1.30, it sounds like SDM failure to me. If you have a Pentax shop near you, take it there and check on current bodies. It will eliminate the K20D or the DA50-135 as the possible cause.

QuoteOriginally posted by pete-tarmigan Quote
Does the firmware version currently installed allow operation of SDM lenses?
That's only relevant for a K10D

05-10-2012, 11:41 PM   #9
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Have you verified that the camera body is set to AF (as well as the lens)?

The K20D supported SDM from the beginning, so the firmware version is not at issue.
05-11-2012, 09:01 AM   #10
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Today a colleague came over with his K10D with the firmware 1.0. ( never been upgraded ). We tried my lens on this camera and it worked perfectly. Then we upgraded the firmware on it and yes, lens stopped auto focusing! Now obviously i need to downgrade my K20D but not sure if i can do it, especially without doing something wrong. Anyways, now at least i know the reason.
Thank you very much for your help and ideas.
05-11-2012, 08:21 PM   #11
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QuoteOriginally posted by Yasar Quote
Today a colleague came over with his K10D with the firmware 1.0. ( never been upgraded ). We tried my lens on this camera and it worked perfectly. Then we upgraded the firmware on it and yes, lens stopped auto focusing! Now obviously i need to downgrade my K20D but not sure if i can do it, especially without doing something wrong. Anyways, now at least i know the reason.
Thank you very much for your help and ideas.
If you search this Forum for your lens you will see that the symptoms are classic: the lens is failing.You won't be able to "downgrade" the K20D so that it auto-focuses without the SDM . You should send the lens in for repair, if the warranty is still good, or you can still manual focus with it if you find the repairs too expensive. I believe that Pentax will give you an estimate first. If they don't volunteer an estimate, ask for one. Repairs to SDM lenses can be expensive.

Good luck. Mine still works after three years, but this lens is known for failures.
05-11-2012, 11:11 PM   #12
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Sorry to butt in, I don't have anything relevant to add, but was curious- if DA* 50-135 has both SDM and screw-drive AF, why can't it AF on K20d with the screw-drive instead of SDM? Is that just how the K20d is?
It was able to work with screw-drive on ist DS, compared to my DA* 55 (which is only SDM only, no screw-drive) doesn't AF at all.
05-12-2012, 11:58 AM   #13
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QuoteOriginally posted by Julie Quote
Sorry to butt in, I don't have anything relevant to add, but was curious- if DA* 50-135 has both SDM and screw-drive AF, why can't it AF on K20d with the screw-drive instead of SDM? Is that just how the K20d
Any Pentax dSLR that supports SDM will not allow usage of screwdrive if it detects a SDM lens. There have been numerous request 'to Pentax' in threads here to change it so the user can choose SDM or screw drive for those lenses.

And it is possible to 'damage' a K20D so it will use screw drive instead of SDM; see https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/85877-i-broke-...t-happier.html by Peter Zack
05-12-2012, 05:10 PM   #14
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QuoteOriginally posted by sterretje Quote
Any Pentax dSLR that supports SDM will not allow usage of screwdrive if it detects a SDM lens. There have been numerous request 'to Pentax' in threads here to change it so the user can choose SDM or screw drive for those lenses.

And it is possible to 'damage' a K20D so it will use screw drive instead of SDM; see https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/85877-i-broke-...t-happier.html by Peter Zack
That really would be a great thing to have. Thank you very much for the info!
05-15-2012, 06:27 PM   #15
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QuoteOriginally posted by sterretje Quote
And it is possible to 'damage' a K20D so it will use screw drive instead of SDM; see https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/85877-i-broke-...t-happier.html by Peter Zack
I was aware of this, but I couldn't recommend that the OP damage his camera. I suppose, now that K20Ds can be had for so little, replacing it could be easy and less expensive than repairing or replacing this lens, if your "fix" of modifying the camera turned out to be more destructive than you had hoped. If my 50-135 SDM dies, I think I would rather use manual focus (it's easy enough to do with this lens) rather than cripple a gem of a camera, no matter how cheap it is to replace today. But that's just me.

Last edited by snofox; 05-15-2012 at 06:34 PM.
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