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12-19-2011, 04:51 PM   #1
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DA 50-200mm Won't Focus Infinity

I recently purchased a Pentax DA 50-200mm lens from B&H and it seems to have difficulty focussing to infinity with K-5 body. Like if I point it at the moon or a distant mountain, it won't auto focus. Fine if I use manual, but ...

Anyone else experienced this? Fixes?

12-19-2011, 04:55 PM   #2
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Moon is pretty hard to focus on, unless it's bright day out. At night, all the k-5's system will see is one giant white blob and it can't resolve anything to focus onto. As far as mountain goes, can you post a sample shot of what you are trying to shoot? And exif too, unless you can tell us what AF type you were using and how you were trying to focus.
12-19-2011, 05:03 PM   #3
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I don't think this is the lens's fault, as the slower the lens, the less accurate the AF (generally speaking), but try setting your camera to use the center AF point and see if that helps. Another possibility is that your lens is back-focusing, in which case you may need to adjust it as per this article:

https://www.pentaxforums.com/reviews/lens-align-front-back-focus/introduction.html

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12-19-2011, 05:05 PM   #4
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There has to be a break on contrast for the body to focus - as JinDesu noted, white blobs you won't be able to focus on; any large area of the same flat color (a group of backlit trees with a dark backdrop is another example) will be difficult to focus on - MF is really the only way to go in these conditions...

12-20-2011, 07:07 PM   #5
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2 Examples MF vs AF

Example 1, Manual focus, lenses/camera would NOT focus on mountains.

Example 2, Auto focus, lens/camera WOULD focus, I guess because of the horizontal vs landscape layout.

EXIF data with photos.

Now putting these here, I rather like them. Which one do you all like best, and how would you improve them. I did 0 post-processing, straight export from RAWs in Aperture. The landscape mode has nice lines in it and depth, I think. The vertical one seems shortened and flat.

These are the mountains one sees west of Hoosier Pass, a few miles above Breckenridge, Colorado, USA.
12-20-2011, 07:18 PM   #6
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The exifs are missing:

Focus mode and focus point select info, so if you can let us know - is it center point focus? Did you aim for the mountains and recompose? The best way to get infinity focus with the mountains is probably to set center point and then to aim your middle of your circle at where the mountain hits the horizon, or where the dark and the light parts of the mountain have the divide. The cross type focusing point in your camera needs to see a contrast.

As far as critique goes - the horizontal one is better exposed, the vertical one is overexposed by a bit. I would say the horizontal one is better composed because the vertical one cuts out too much mountain. I wouldn't do much post processing.
12-20-2011, 10:39 PM   #7
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The photos were take with matrix focusing, 11 point, not center. Using center is s good idea. I am guessing with the trees and the mountains at different distances, the matrix didn't know which to focus on.

As for exifs, if when looking at the pic in Flickr, you go to Actions>view exif info, you'll see it. Although it does not state focussing method or any lens info, i am guessing because that comes from the lens, not the camera and image file.
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