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02-29-2012, 04:37 PM   #1
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Pentax 16-50mm Won't Lock Focus

Hello, i have a problem with my Pentax 16-50mm lens. The lens won't lock when in AFS, it just does NOT lock on target in autofocus at all. The lens was tried in two different cameras and still the same problem. I had dropped the lens back in the summer and just now got it repaired by Eric Hendrickson, which was highly recomended in the Forums here. So i got my lens tried it, did not want to lock on target in A/F then sent it back, Eric told me that he rechecked it, and tried it, and it focused and locked on target with his camera. Now i bought a brand new K-5 just to see what is wrong, and honesly the lens wont LOCK on target. I don't know what else to do, do you guys have any recommendations to get it to lock on target in AFS? Help would be highly appreciated! Thanks alot!


Last edited by A.M.92; 02-29-2012 at 05:22 PM.
02-29-2012, 06:22 PM   #2
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Camera as well as lens are set to autofocus, right? Perhaps you could meet up with another Pentaxian in your area and try on his/her camera?
02-29-2012, 06:29 PM   #3
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If you have tried it on two different cameras, looks like you have tested it well. Are you sure the lens is in AF? There is a switch on the side. Good suggestion above to meet with someone local with a known good camera, or even another copy of the 16-50 to try on your camera. Something sounds like it is set wrong, but I cannot imagine what except the AF/MF switch on the lens. You might try it in both modes just to test.
02-29-2012, 07:03 PM   #4
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I have tried it with another K-5 from another "Pentaxian" , now i purchased a brand new K-5 to see if it was perhaps do to the camera body, but the same problem is persistant, the lens just hunts, goes from infinity to infinity does not want to lock on any subject whatsoever. Don't know what else to do, i am convinced that the lens was not repaired correctly but then why does it AF but refuses to LOCK ON, that is strange perhaps something is not in contact, any ideas?.. Thanks for the replies!

02-29-2012, 07:03 PM   #5
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QuoteOriginally posted by Ole Quote
Camera as well as lens are set to autofocus, right? Perhaps you could meet up with another Pentaxian in your area and try on his/her camera?
Yes that is correct, both are in AF..
02-29-2012, 09:37 PM   #6
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QuoteOriginally posted by A.M.92 Quote
I have tried it with another K-5 from another "Pentaxian" , now i purchased a brand new K-5 to see if it was perhaps do to the camera body, but the same problem is persistant, the lens just hunts, goes from infinity to infinity does not want to lock on any subject whatsoever. Don't know what else to do, i am convinced that the lens was not repaired correctly but then why does it AF but refuses to LOCK ON, that is strange perhaps something is not in contact, any ideas?.. Thanks for the replies!
Not much left to do than sending the lens to an authorized Pentax service center, I'm afraid.

It focuses correctly on Eric's camera, perhaps that's with the screw-drive mechanism, and it fails with your camera which is using the motor in the lens. That could be the difference.
03-01-2012, 05:58 AM   #7
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That could be it, something in the lens is not working properly. I've spent already almost 300$ for the repairs that i was charged by Eric, at this point i don't know if it's worth sending it in to somebody else..
02-15-2015, 06:46 AM   #8
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Howdy old thread! haha

I have a DA* 50-135mm that I'm convinced has the same problem. I did try a few things that might add to the discussion and maybe some people could then help us (the people with such problems) find a solution!

The problem : The lens won't lock focus at most focal lengths - it just hunts back and forth and eventually gives up. At around 70mm though, it locks quickly and precisely.

What I know and tried :
- The lens focus well (produces sharp picture) from minimum focussing distance to infinity using MF.
- The problem is the same using screwdrive focus and SDM (I tried both)
- The problem remains on two different perfectly working K-5II
- Contacts are clean as far as I can tell
- Lens takes sharp pictures (at least in the middle (I don't check borders much on this lens since it's mostly a lens I use for portraits and such, were the subject is in the middle of the frame)
- Lens is in good condition, I can't hear anything suspicious when I move it gently from side to side.

Where it gets interesting :
The lens will focus perfectly (AKA no hunting at any focal lengths) when I use live view (I use the second mode, contrast detect I believe?)

So, anyone has an idea on what I could do or about what the problem might be?

Karl

02-15-2015, 07:04 AM   #9
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Are you sure it is not back/front focusing? If it is doing one of either it will never lock onto focus.. it will just keep racking back and forth never finding a home.

The 16-50 was, at a time, known for back focusing quite a bit. My copy also back focuses and I had to correct by +5 to get it to lock into view. Actually, after +2 it started locking focus. But +5 is really sharp. Your copy might need a bit of adjustment too.
02-15-2015, 11:53 AM   #10
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QuoteOriginally posted by mee Quote
Are you sure it is not back/front focusing? If it is doing one of either it will never lock onto focus.. it will just keep racking back and forth never finding a home.

The 16-50 was, at a time, known for back focusing quite a bit. My copy also back focuses and I had to correct by +5 to get it to lock into view. Actually, after +2 it started locking focus. But +5 is really sharp. Your copy might need a bit of adjustment too.
Although I have a 50-135mm, not a 16-50mm, your point is very interesting. I didn't know that front or back focus could cause such problem. I will check that right now! Thank you for your input.

Edit : I tried + and - adjustments, no luck.
Also, upon further inspection, the lens won't lock focus at focal lengths longer than about 92mm, and appears to function perfectly between 50-92mm. Strange.

Last edited by kp0c; 02-15-2015 at 12:01 PM.
02-15-2015, 01:07 PM   #11
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That's strange, as my SMC DA* 16-50mm/2.8 with K-3 Live View travels all the way focusing first to infinity then to minimum [focusing] distance, then goes back to 'middle' and locks on target. Every time the above pattern, like with old P&S. I'm guite fed-up as the above means at least half a second lost, and then you loose your subject quite often.
BTW earlier today I tried to micro-adjust the DA* 16-50mm in K-3 menu; there was improvement in sharpness from '0' to '+5' settings, than no improvement from '+5' to '+10', when I had a feeling the lens needsfurther '+15' or so. I left with '+5' adjustment for further trials.

-----
QuoteOriginally posted by kp0c Quote
The lens will focus perfectly (AKA no hunting at any focal lengths) when I use live view
02-15-2015, 04:10 PM   #12
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I should have been more precise when I talked about live view focussing. The lens will indeed go past focus point then come back and lock focus, but that is my experience with any lens using live view, thus the "perfect" qualification.
02-16-2015, 12:36 PM   #13
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