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07-18-2015, 04:31 PM   #1
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Focus issue with DA 50mm 1.8 and K3

Last night I took some pictures of teens on a climbing wall using my new K3 and DA 50mm 1.8. When I got them on the computer I noticed faces were out of focus and the focus seemed to be closer. Here was my set up:

Single point focus moved to the left of center two spots, on the edge of the 5x5 box. The I turned the camera clockwise 90 degrees so that when I put this focus point on the climbers face the rest of their body would be in the picture. It is, for this, a perfect set up. I have one example from last night and three shots from today that I took as a test. The three test shots are:
  1. center point focus on the base of the hand-hold
  2. single focus point moved to the RIGHT two spots and the camera turned counter clockwise - focuse is pretty good consider it is about half way from center of the lens.
  3. Last one is what I was using. center point moved left two spots and the camera turned clockwise 90. Really bad focus and the actual focus is closer to the camera.

The last photo is an actual photo from last night and can see the focus is not on the face but lower (i.e. closer) to the camera.

So is this a lens issue? Or is it a possible an issue with the one focus point not properly focusing? I have my k50 and could do the same test with it if necessary. In the worst case I the the alternate focus point and rotate 90 opposite of what I am used to but I know this is going to bug me until I figure out what is up. Thanks for any help









07-18-2015, 11:01 PM   #2
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Front / back focus issues are easy to identify. I mount my camera on a tripod and point it downward at 45 degrees. Place a flat piece of paper with text on it so the text runs vertically in the frame. Get close to the minimum focus distance. Wide open aperture. Good lighting. ISO 100. Take a picture. Zoom in on your preview in your LCD to 100%, 8.3x view. The center of your image with a very thin depth of field should be in focus. I suppose you can use this set up and move the focus points around. Just make sure to defocus your lens and let the camera refocus it. Sometime a soft image is still sharp enough for the AF system to think it's in focus. When I photograph consecutive images in non-burst mode I always try to get the camera to refocus vs. confirming previous focus.
07-19-2015, 05:46 AM   #3
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I think part of the problem is you're shooting at f2.2, not much DOF at that aperture. Also, the blurriness you see looks to me like subject movement more than a focus issue.

Of course, that's just my opinion, I could be wrong.
07-19-2015, 02:41 PM   #4
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QuoteOriginally posted by 6BQ5 Quote
Front / back focus issues are easy to identify. I mount my camera on a tripod and point it downward at 45 degrees. Place a flat piece of paper with text on it so the text runs vertically in the frame. Get close to the minimum focus distance. Wide open aperture. Good lighting. ISO 100. Take a picture. Zoom in on your preview in your LCD to 100%, 8.3x view. The center of your image with a very thin depth of field should be in focus. I suppose you can use this set up and move the focus points around. Just make sure to defocus your lens and let the camera refocus it. Sometime a soft image is still sharp enough for the AF system to think it's in focus. When I photograph consecutive images in non-burst mode I always try to get the camera to refocus vs. confirming previous focus.
But is only near focuses when using the specific point on the left. :-( Center point and far right points focus correctly.

---------- Post added 07-19-15 at 02:46 PM ----------

I hear what you are saying and would probably have thought the same thing. But what I found out it is 100% off focus with the focus point on the left. It never does that with center focus or the point on the opposite side. I can replicate it all day hand held. Even on a tripod I get the same out of focus result with only the one point.

I don't generally go looking for issues but just noticed when processing a lot of photos that the focus was closer on all of them. So I went back the next morning and was able to replicate the shots you see above. One of the reasons for using 2.2 is that it is dark where that wall is in the evening and you have to shoot with a low aperture to have a reasonable shutter speed to avoid blur.

QuoteOriginally posted by Al_Kahollick Quote
I think part of the problem is you're shooting at f2.2, not much DOF at that aperture. Also, the blurriness you see looks to me like subject movement more than a focus issue.

Of course, that's just my opinion, I could be wrong.


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