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02-24-2008, 09:24 AM   #1
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AF won't lock with DA*16-50 - occasionally...

Hi,

I think this is a problem I haven't heard before.

It started yesterday but that was a very dark and grey day so I let it go by.
Today however was a very sunny day and it happened again. Strangely, at 16mm there didn't seem to be a problem. Any longer length refused to lock.
I removed the lens and attached it again and that seemed to help - for a while.

It's a kind of of/on situation: I just tested in my living room which is pretty dark right now and it locked without a problem.

Any ideas or suggestions?


ps used on K10D with 1.3 firmware

02-24-2008, 09:28 AM   #2
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Maybe the contacts aren't properly connecting to the body. Also, try different focus modes.
02-24-2008, 11:13 AM   #3
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A problem with the contacts was my guess as well. That is why I tried with re-mounting the lens. It seems to work, for a while.
What is strange to me, is that this lens gave no problem since I got it (December 24th 2007) for some 500 shots.

For focussing, I allways work with the central focus point selected.
02-24-2008, 12:13 PM   #4
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It might have taken a fall or something, and you may not know about it, then. Five hundred shots is a good number of shots, and this seems random. Maybe it's an issue with your body. Have you tried other AF lenses?

02-24-2008, 12:48 PM   #5
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I've used the 16-50 for the most part since I'm currently also evaluating DxO V5.04 with the new module for this lens and the problem occured only yesterday.
I'll try some other lenses extensively as soon as I get a chance. Work takes priority, I'm afraid.
02-25-2008, 12:53 PM   #6
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SDM or drive screw?

Since yesterday evening, at every attempt I made, the af did lock.
However, I read about some 50-135s that "reverted back" to using the AF drive srew rather than the SDM. It apears to be a problem in the body.
Any ideas on how to verify which is being used?
02-25-2008, 01:39 PM   #7
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QuoteOriginally posted by Bart Quote
Hi,

I think this is a problem I haven't heard before.

It started yesterday but that was a very dark and grey day so I let it go by.
Today however was a very sunny day and it happened again. Strangely, at 16mm there didn't seem to be a problem. Any longer length refused to lock.
I removed the lens and attached it again and that seemed to help - for a while.

It's a kind of of/on situation: I just tested in my living room which is pretty dark right now and it locked without a problem.

Any ideas or suggestions?


ps used on K10D with 1.3 firmware
Bart, I've made approximatly 1000 photos with my K10D & 16-50, using 1.3 firmware.
It never refused to lock focus except in some very rare cases with surfaces without contrasts.

- Bert
03-09-2008, 07:41 AM   #8
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Still on and off problem

Yesterday, I finally got the chance to go out in the field again.
When I tested before around the house from time to time, I had no problem at all.
Also with some non-SDM lenses, I didn't find any problem at all.

In the field however, it happened again. Afther a while the camara wouldn't lock focus on items with plenty of contrast and only in the longer focal lengths.
I switched to a non-SDM lens and no problem to lock on the same subjects (a tree and a barn).
When I switched back to the 16-50, again there was no problem.

Do you think I should send it in for service? If so, what? Body and/or lens?
With my luck, the problem probably won't produce itself when at the pentax service center.

03-09-2008, 07:30 PM   #9
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QuoteOriginally posted by Bart Quote
Yesterday, I finally got the chance to go out in the field again.
When I tested before around the house from time to time, I had no problem at all.
Also with some non-SDM lenses, I didn't find any problem at all.

In the field however, it happened again. Afther a while the camara wouldn't lock focus on items with plenty of contrast and only in the longer focal lengths.
I switched to a non-SDM lens and no problem to lock on the same subjects (a tree and a barn).
When I switched back to the 16-50, again there was no problem.

Do you think I should send it in for service? If so, what? Body and/or lens?
With my luck, the problem probably won't produce itself when at the pentax service center.
Hi, Bart. Before losing the use of the lens while Pentax repairs it, take some methylated spirits (alcohol) and a microfiber cloth and apply them to the contact areas of the lens. Don't forget the two contacts down inside the mount - these are the SDM contacts (or Power Zoom with some lenses).
03-09-2008, 08:42 PM   #10
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Maybe this is why. To quote Tom Lusk from https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/22147-do-i-hav...16-50-a-4.html

"And, sadly, based on a credible report on DPR a while back, there will be lens failures with this model in the future - possibly many of them - due to rough finishing on the inside of the barrel and a substandard plastic piece (a guide, I believe), also inside, that will cause the focussing mechanism to fail. One example of this type of failure has just been reported. "
03-10-2008, 01:49 AM   #11
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Another possibility is testing a new battery.
There are reports and I have experienced this as well, that when the battery is low or very old, AF has its problems.
03-10-2008, 04:31 AM   #12
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Thanks for the replies!

Battery shouldn't be the cause: Saterday, I was using a freshly charged battery. Both are less than a year old (still quite new to digital).

Cleaning the contacts might be a possible answer since re-attaching the lens seems to solve the problem for a while. However, I wonder if they could be in need of this operation already.
I'll give it a try for sure.

If it would be caused by a part that is broken, then I guess it would never work anymore?

It's a pitty really because otherwise, I think it's quite a good copy.
There is another thing I noticed: when I set the zoom to a certain value (say 43mm) and I walk around, the zoom changes by itself (zoom creep?). I don't know if this is to be expected. I never did this before with the kit lens or the 50-200.
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