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06-03-2013, 01:53 PM - 1 Like   #16
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The focus and sharpness is almost perfect near the ground for the three rightmost girls and so are the skirts of the two rightmost, so it seems the focus is at around that plane. But then there are some strange things going on.
1. The second (from right) girl's face should be in about that same plane so should also be pefectly in focus.
2. Looking at the Nike logo on the shoe of the guy on extreme right there is what looks like a very pronounced left-right motion blur, This is very odd for a 1/2500 shutter speed. On his cap it is even worse
3. This blur can also be seen in the red and white stars just above the feet of the leftmost girls. This is even more odd as their feet are certainly not moving and any camera motion would show up on all the photo.

The only thing I can think of is some problem with the lens, usually this would be a misaligned element. The apparent motion blur is probably a result of that rather than actual blur.

If I understand correctly the lens has IS but it was switched off.. What could very likley be happening is that either the movable element (the one that does the stabilising) is not being properly 'parked' when you turn off the IS and/or it has some problems with its bearings, allowing it to move axially on one side. Whether or not you get sharp photos could just depend on where the IS element happens to settle down. Depending on the exact mechanism used in the lens the incorrect parking could itself result in axial misalignment even if there is nothing broken in the lens.

Check the lens manual about turning on/off the IS. On a Sigma lens I have it tells you specifically to only turn on/off the IS while the camera is powered up, and it seems important to do so. I guess it has to do with the lens needing power to properly park the IS element. I think though that they might be missing an important detail, at least as far as Pentax SLRs are concerned. The Pentax cameras I have (k-r and K-30) both remove power completely from the lens as soon as the exposure meter turns off, so to ensure that the lens properly parks I think you need to not just have the power on but also have just half pressed the shutter to activate the exposure meter and hence also provide power to the lens.

Check also from time to time if there is any rattling in the lens. You will have to do this with the lens removed though as otherwsie the normal rattling of the K-30's sensor will make it impossible to tell. Unlike the K-30s sensor which becomes free to move when powered off the one in the lens should be locked solid when powered off.

Perhaps I should have asked first thing, is it only with that lens that you get this problem? If you're geting the problem also with non-IS lenses then nearly all I said in this post was useless


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