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04-22-2013, 05:53 AM   #1
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k-5 II and AF on DA 55-300mm Zoom Lens

Hi there

Hopefully somebody will be able to help me. When I use my DA 55-300mm Zoom Lens on the K-5 II, the autofocus keeps on hunting without being able to focus when taking a picture through the viewfinder. Strangely, if I use «LiveView», the lens works as it should be.

If I use this same lens on my Kr, everything's perfect and if I use another lens on the K-5 II (DA 18-135mm WR), everything's perfect as well...

Thanks in advance for any help/hints you can offer. I was trying to shoot sports this weekend but couldn't use this lens

04-22-2013, 06:14 AM   #2
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I don"t really have an explanation as to why this is happening but do you experience this behaviour in 100% of the shots you tried or just in some? I noticed it helps a lot with the 55-300, if you manually move focus close to being right and let the autofocus do the rest, especially if the image is completely out of focus (like when you move from a very close to a far away subject).
04-22-2013, 06:25 AM   #3
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What focus mode are you using? Did you turn on expanded AF?
04-22-2013, 07:04 AM   #4
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Indeed, the focus «catches» sometimes in really bright conditions and at the shortest focal length. I tried both AF.s and AF.C and Expanded AF is turned on.

04-22-2013, 07:13 AM   #5
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What subjects? Any subjects? Do you have any example images where it locked focus (whether accurately or not)?
04-22-2013, 07:25 AM   #6
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Any subjects. Here's one at 55mm where the AF «caught» on the white border of the window, but could not on the brick wall. At 300mm it wouldn't focus on anything at all...
04-22-2013, 08:11 AM   #7
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The 55-300 is a "slow" lens. At 300 mm your aperture is at f/5.8 and you are at the limits of the AF module's abilities. I wonder if the front/back focus adjustment could help the lens focus a bit better. I don't have that capability with the K10d, but it might enhance the contrast a bit.

Some ideas (that others will probably shoot down, but it won't be the first, nor the last, time).
- Remove any filters on the front of the lens.
- Always, always, always use a lens hood
- Shade the lens with your hand if the hood isn't enough (at the long end, it isn't)

Good luck.
04-22-2013, 09:01 AM   #8
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Thanks all for your input. I've just been able to test the k-5 II with a friend's 55-300 lens identical to mine and the problem did not occur... I'll send my lens to Pentax today. Why it works on the Kr though is a mystery...


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