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03-20-2013, 08:36 AM   #1
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DA* 50-135 issues

Hi all, I was wondering if anyone has had this same problem:
I was calibrating my lens for the first time because I noticed it was back focusing, so I changed the autofocus adjustment to -10 (which seemed like a lot) and this helped a lot... but only at the 50-70mm point. My main concern is when I focus in on an object at 70-135mm it doesn't focus well. Everything is a little fuzzy. Not sharp at all. Should OI be sending this lens in for maintenance or is there something I can do to fix this issue? HELP PLEASE!!

03-20-2013, 08:41 AM   #2
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What made you arrive at a -10 adjustment? What were the specifics of your controlled testing?
03-20-2013, 09:00 AM   #3
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With camera on a tripod, I placed a focus chart parallel to the sensor (the lens point to it at 90 degrees) and next to it I had a ruler at 45 degrees with the "focus" line intersecting the focus chart. I used the 45 degrees chart to see where it actually achieved best focus. I then adjusted the camera to correct for front/back until I got an image when both the vertical card was in perfect focus and the DOF on the ruler was equally distributed from the center focus line. I've done this with other lenses and its worked fine. Like I saiud, with the -10 adjustment I can get perfect sharp focus at the point I am aiming at when the lens is set between 50-70 mm, 70-135 is just fuzzy. am I doing this wrong?? ugh.
03-20-2013, 09:27 AM   #4
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It looks like you are doing a good test. The reason I asked is that some folks will just randomly change the AF adjustment and wonder why it isn't working.....

Zooms are thought sometimes - in my experience if you get it right at one end, the other is then off. You either have to adjust to which end you use the most, of settle for a compromise. My DA* 50-135 was right on throughout the range on my K-5 as is my DA* 60-250.

One thing of note to add here - I just sent my second K-5 in for service for the camera itself back focusing. I thought I was going nuts both times when I was running into a similar situation as you are. If you have a good prime, I would run your test on that lens first to maybe see if it might be the camera. If the camera checks out OK, it might be worthwhile to send both camera and lens in for calibration.

03-20-2013, 09:34 AM   #5
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Thanks so much, this helps! I will try testing a prime and see what happens.
03-20-2013, 12:17 PM   #6
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I had the exact same problem with my 50-135 so I sent it in (drove it in actually) to Pentax in Mississauga ON and had it calibrated to my K-5. It is perfect now, no adjustment needed. All my other lenses (11 more) are and always have been fine.
03-20-2013, 01:09 PM   #7
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Sounds like a calibration would help, my brother has one that was bad at 135mm but after adjusting it's perfect.
03-20-2013, 03:21 PM   #8
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So if I send it in to Pentax, should I send it along with my camera? I'm going to do some tests with my other lens' first to see if its just my camera...

03-20-2013, 03:24 PM   #9
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Yes, Pentax wants your camera as well, and if you are lucky like I was, they will give it a CLA while they have it. Mine came back as clean as new!
03-20-2013, 04:09 PM   #10
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Awesome! Thanks for the info!!
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