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06-22-2021, 05:43 PM   #1
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Why would a lens work on one K5 body and not another?

I picked up a Sigma APO 135-400mm f4.5-5.6 lens for a song last week and it finally arrived today in the post. I was concerned that it was too cheap to be working, and when I attached it to me my K5 body the AF didn't work at all. It sounds like the screw drive isn't attached to the lens and it is just spinning freely. My other K5 body, works just fine. Both bodies have the 1.16 firmware, and looking at the contacts and screw drive mechanism, they both look the same. Anyone experienced something like this and have any suggestions on what may be the issue or how to fix it?

Darryl

06-22-2021, 05:51 PM - 1 Like   #2
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Some times the screw drive does not engage. I have this issue when sepwitching back and forth with my 70-200/2.8 between my K10 and PZ1. What you can do is set the body to Mf and then focus manually. Maybe the drive will drop in and engage, then put the body back in AF
06-22-2021, 05:54 PM   #3
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QuoteOriginally posted by Lowell Goudge Quote
Some times the screw drive does not engage. I have this issue when sepwitching back and forth with my 70-200/2.8 between my K10 and PZ1. What you can do is set the body to Mf and then focus manually. Maybe the drive will drop in and engage, then put the body back in AF
If I switch to manual focus, it is a little stiff, but focuses okay. Switching back to AF-S or AF-C just spins the wheels...
06-22-2021, 06:24 PM - 1 Like   #4
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I've set the af/mf switch halfway between the two, the result is not a joyful noise. Never had it spin without engaging at least partially though..

06-22-2021, 06:55 PM - 1 Like   #5
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Look at the screw face clearances on the two cameras with the lens removed and the cameras in AF mode (compare the two) and see if there is any difference.
06-22-2021, 07:03 PM - 1 Like   #6
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Just thinking. I could be the screw drive contact point is very slightly worn more one camera, or the lens, or both, not allowing the screw drive to fully engage.
06-22-2021, 07:48 PM   #7
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QuoteOriginally posted by Bob 256 Quote
Look at the screw face clearances on the two cameras with the lens removed and the cameras in AF mode (compare the two) and see if there is any difference.
QuoteOriginally posted by DWS1 Quote
Just thinking. I could be the screw drive contact point is very slightly worn more one camera, or the lens, or both, not allowing the screw drive to fully engage.
it wasn't as noticeable without employing a magnifying loop, but the one K5 body that works has about 0.5mm more extension of the screw drive contact than the other one. I assume that's unlikely to be an easy fix though... But it does explain the difference between the two. Thank you!

06-22-2021, 08:19 PM - 1 Like   #8
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QuoteOriginally posted by SointulArt Quote
it wasn't as noticeable without employing a magnifying loop, but the one K5 body that works has about 0.5mm more extension of the screw drive contact than the other one. I assume that's unlikely to be an easy fix though... But it does explain the difference between the two. Thank you!
It *might* be an easy fix though if it is just got some crud in it or something -- just flipping the AF/MF switch back and forth a number of times (with no lens mounted) might loosen it up (or just gently tug on it when extended and see if it will extend more).
06-22-2021, 08:30 PM   #9
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QuoteOriginally posted by vonBaloney Quote
It *might* be an easy fix though if it is just got some crud in it or something -- just flipping the AF/MF switch back and forth a number of times (with no lens mounted) might loosen it up (or just gently tug on it when extended and see if it will extend more).
I've tried for 20 minutes and it seems as if it isn't going to magically pop up that extra little distance so it can work. Probably time to think about saving my pennies for a new body anyway...

Darryl
06-23-2021, 03:36 AM - 1 Like   #10
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QuoteOriginally posted by SointulArt Quote
it wasn't as noticeable without employing a magnifying loop, but the one K5 body that works has about 0.5mm more extension of the screw drive contact than the other one. I assume that's unlikely to be an easy fix though... But it does explain the difference between the two. Thank you!
Lack of extension of the screw drive is linked to the lens release button. When you press the lens release, it also retracts the screw drive. Is the lens locking pin extending out fully. You might be able to resolve this by unscrewing and removing the mount and checking there is nothing obstructing the release mechanism
06-23-2021, 03:48 AM - 1 Like   #11
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Lots of knowledge and experience shared on this thread, thank you
06-23-2021, 05:53 AM   #12
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QuoteOriginally posted by Lowell Goudge Quote
Lack of extension of the screw drive is linked to the lens release button. When you press the lens release, it also retracts the screw drive. Is the lens locking pin extending out fully. You might be able to resolve this by unscrewing and removing the mount and checking there is nothing obstructing the release mechanism
Thank you, it seems as if it is not extending as much as the other body, so this is something I will explore.
06-23-2021, 10:24 AM - 1 Like   #13
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Doesn't the Sigma Pentax mounts have a slight reputation for being finicky. In that case I guess the bright side is it works on one of the bodies.
06-23-2021, 11:45 AM - 1 Like   #14
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Sounds like the cause may have been nailed. I was just wondering though - do other screw drive lenses work on the body that's giving the problem? If they do, you might also compare the screw drive port on the back of the Sigma lens to other lenses and see if the depth of the mechanisms are exactly the same. Could the Sigma mechanism be 0.5mm more recessed?
06-23-2021, 12:43 PM   #15
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QuoteOriginally posted by Apet-Sure Quote
Sounds like the cause may have been nailed. I was just wondering though - do other screw drive lenses work on the body that's giving the problem? If they do, you might also compare the screw drive port on the back of the Sigma lens to other lenses and see if the depth of the mechanisms are exactly the same. Could the Sigma mechanism be 0.5mm more recessed?
Good question, which will have to wait a little while before I can try other lenses, as I only have this one screw drive lens with me at the moment.

Darryl
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