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06-08-2017, 06:41 AM   #16
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Yes, thanks. I read that article. Meanwhile, I did some more testing. On a level tripod. This time, I changed apertures. Here it is at 135 f/4:

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06-08-2017, 07:58 AM   #17
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What is your distance to the target? And what is the expected depth of focus at that distance?
06-08-2017, 05:26 PM   #18
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Have you tested your lens with real-world picture-taking? You may find the anomalies to be so slight as to make repair unnecessary. I'm not saying there isn't an issue - the left side looks soft to me too. But one sure way to find a problem is to go looking for problems. Every lens will show some weakness under enough scrutiny. Only a real-life test will tell you if those weaknesses are large enough to worry over.
06-09-2017, 02:45 PM   #19
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Good advice! Will report back on that.

06-09-2017, 06:03 PM   #20
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QuoteOriginally posted by abruzzi Quote
The idea is you print the document below, focus on the page, then defocus a little. If it deforms shape when it blurs (i.e. becomes oval instead of circular) the lens is decentered. Is there a drawback to that method?
The target has the be perfectly flat and aligned with the camera parallel to the target and aligned with the center optical axis - otherwise you can get a false positive. I use the star chart with an optics testing bench, testing lenses through a camera is just adding to the number of variables that can make lens testing difficult - a dedicated optics bench can reveal flaws and give you the ability to quantify them which is something that can be difficult to do with just a camera. Having an optics bench also allows me to develop profiles for my own lenses - sometimes due to manufacturing tolerances canned profiles can be inaccurate, which is often the case for some zoom lenses at specific focal lengths.
06-14-2017, 11:45 AM   #21
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Unfortunately, I'm seeing the same issue when I take shots outside -- the left side of the image is not nearly as sharp as the right side. I wish Precision Camera, which is about an hour and a half from me, had a better reputation for repairs since they're the authorized service facility for Pentax in the US. Unless someone has a better suggestion.

Amy
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