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07-30-2010, 10:10 AM   #1
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K-7 and 50-135mm focusing problems

So, I know this has been covered many times before, but here's my latest problem relating to focus with the K-7.

Last night, I finally had a chance to download and print that focus chart from focuschart.com. After starting to set things up, I realized very quickly that you need to be quite close to it use it. So, I set my 50-135 up about 4 or 5 feet from the chart (which was placed on a table), at about a 45 degree angle. Starting taking some shots, and realized it was more or less consistently off. So I adjusted AF a few times, and ultimately ended up settling on -2, which gave more or less consistent properly focused shots.

Here's the problem: I then took the camera off the tripod, and took a picture of a can about 3 or 4 feet away. No problem - properly focused. But then, when I tried to focus on something further away - say 10 or 15 feet, the focus was totally off again, consistently. So, just to use something flat, I took the focus chart and taped it to a wall, and took pictures of it (not at a 45 degree angle; just more or less perpendicular to it). Sure enough, it was noticeably OOF again. After fiddling some more with AF adjustment, I decided that +5 was consistently giving the best results at that distance.

So WTF gives??? I've suspected this before (and have talked about this in previous posts), but it seems like it does in fact focus differently at different distances. Now, not every part of this test was perfectly scientifically set up, but I think it's pretty obvious that this is in fact what's going on. Is this normal? Should I send my lens/camera in for repair, or is this just a common characteristic of this particular camera or lens or camera/lens combo? It's super frustrating, as it leaves 0 confidence in the ability to get properly focused shots in a dynamic setting, such as when photographing events (an application for which the 50-135 is by far my primary lens, due to its range and max. aperture).

Any thoughts?

07-30-2010, 10:47 AM   #2
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My gut reaction here is that your lens is fine and doesn't need to be adjusted- but that's just me.

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