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06-25-2013, 04:16 PM   #1
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No more AF after 70mm

Hi everybody,

New to the PentaxForums, I would like to greet everybody around and bother you with a question.

My good old every time and vacation-lens, the 18-250 Pentax, does not focus any more automatically after 70mm. It just hunts up and down and will stay finally in some blurry position. Concerning the AF, you could say I'm now a proud owner of a quiet heavy 18-70mm lens, as between 18-70mm it still performs as it should. The problem is definitely not the camera as I tried the lens on my K-r and on my K5 II ....same problem. It all started when I tried out such a converter-adapter-thing to mount my lens on the camera-body the other side round to have a macro-lens. That ruined apparently something in my lens. The big question now is : Is it possible to reset a kind of a software in my lens to get it back performing AF from 18 - 250mm ?
It is maybe only a such a stupid and easy thing to do to get it back as it was before !?

Your help is very much appreciated,
Orion

06-25-2013, 04:28 PM   #2
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QuoteOriginally posted by orionschwert Quote
Hi everybody,

New to the PentaxForums, I would like to greet everybody around and bother you with a question.

My good old every time and vacation-lens, the 18-250 Pentax, does not focus any more automatically after 70mm. It just hunts up and down and will stay finally in some blurry position. Concerning the AF, you could say I'm now a proud owner of a quiet heavy 18-70mm lens, as between 18-70mm it still performs as it should. The problem is definitely not the camera as I tried the lens on my K-r and on my K5 II ....same problem. It all started when I tried out such a converter-adapter-thing to mount my lens on the camera-body the other side round to have a macro-lens. That ruined apparently something in my lens. The big question now is : Is it possible to reset a kind of a software in my lens to get it back performing AF from 18 - 250mm ?
It is maybe only a such a stupid and easy thing to do to get it back as it was before !?

Your help is very much appreciated,
Orion
Unfortunately that lens autofocus is screw-drive based - it is mechanical and not software based. What likely happened is that by putting added weight on the front of the lens the internal parts became stressed and dislodged internally, causing the AF failure. I would hazard a guess that attempting to manual focus the lens at longer focal lengths is difficult as well. I think your only remedy is going to be sending it to Pentax for repair.
06-25-2013, 04:48 PM   #3
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QuoteOriginally posted by pxpaulx Quote
What likely happened is that by putting added weight on the front of the lens the internal parts became stressed and dislodged internally, causing the AF failure.
Probably a good opportunity to call this to the attention of would-be reverse-lens macro shooters. A classic A or M variety 50mm reversed for macro shooting is going to be light, mostly metal where it counts, and won't run afoul of the stresses described in the OP's issue.
06-25-2013, 06:27 PM   #4
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But how would you auto focus a reversed lens in the first place???

06-25-2013, 08:11 PM   #5
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QuoteOriginally posted by calsan Quote

But how would you auto focus a reversed lens in the first place???
I didn't realize he reverse mounted the lens like that - that is a large lens! According to the lens database 455g, so right about 1lb. Most of that weight is going to be where the lens is supposed to be mounted, at the back. using a reverse ring mount, then extending it will put major stress on the internal construction, regardless of whether the OP had autofocus or not (in this case I'm guessing they were still using manual focus).
06-27-2013, 03:21 PM   #6
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Hi and thank to everyone thinking about a solution. If I understand correctly, I only could let repair it by a pro and it was somewhat not intelligent to mount such a heavy lens as a macro-lens . Is there maybe even a better all-rounder lens available as the one I have ? The new one (18-270) seems to perform not as well.

Greets,
Orion
07-11-2013, 05:48 AM   #7
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hello

Just wanted to give a simple solution - try to press the lens hard as close to the body as you can, especially the place around the AF screw then duct tape it
the tape will keep the lens and the body close and the AF screw will be happy
07-17-2013, 06:51 PM   #8
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Thank you for the effort but everything fits perfectly and AF anyway works between 28-70mm, so it can not be the problem. Thank you anyway

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