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07-02-2014, 12:44 PM   #1
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DA 18-135 WR AF issue

I recently purchased a DA 18-135 WR lens from a forum member and I am having an issue with it. At short zooms, say from 18-50mm, AF if fine. It captures a target quickly and needs minor or no adjustment for a sharp focus. At longer zooms the AF selects a target, but it is not even close to being in focus. The longer the zoom, the worse the problem. If I manually adjust the focus, I see focus confirmation in the viewfinder but again, the object is not even close to being in focus. It is as if the lens is finding a target in an out of focus plane. The AF problem happens on both a K-5 and a K-x.

Is this a common problem or could the lens be damaged? Is there anything I can do to troubleshoot further? Any help is appreciated - thanks!

07-02-2014, 12:52 PM   #2
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Can you post some samples? The lens could be suffering from front/back-focus or de-centering.

Adam
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07-02-2014, 05:28 PM   #3
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My 18-135 WR seems to work extremely well. No problems of any sort...so far...touch wood.
07-02-2014, 06:14 PM   #4
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Thanks! Attached are three examples. The first two were using auto AF.S, center focus, at 135mm. The focus confirmation in the viewfinder pegged the squirrel. The last picture is auto focus and then fine tuning it manually. I took some shorter zooms too, if you would like to see them. I am beginning to wonder if all zoom ranges are out of focus, but the shorter zooms are less noticeable.

---------- Post added 07-02-14 at 06:15 PM ----------

Then again, I have also heard told on these forums that squirrels are evil and may have cloaking abilities...

Attached Images
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
07-02-2014, 06:37 PM   #5
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If I were an Auto Focus system, to me especially in the second picture, the background colours and contrast of the leaves would be much more tempting to focus on than the squirrel. One thing you got to remember is that the focus point area is larger than the red square implies.

Could also be a back focus problem but I never saw it quite as far off.

But then again, AFAIK I'm not an AF chip...
07-03-2014, 08:59 AM   #6
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Another example of the AF system knowing better what the photographer wants in focus.


Steve
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