Originally posted by BeerBelly Just to chime in my 2 cents here. I first got the lens when I had my K-r and it was brilliantly sharp at all focal lengths and apertures. When I bought my K30, I noticed that at 200mm and f2.8 it was a little soft. I needed to use at least f3.2 to get good sharpness. I then decided to switch to Nikon and wanted the same lens for my D7100. So I bought one and was sorely disappointed. It was soft at 200mm until f5.6. I think this lens hits the resolution limit quite soon. I'd say the APS-C 16Mpix sensor is the upper limit for it. If you decide to get a K-3 in the future be ready to be disappointed.
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Regarding the Nikon switch - If it was 'soft' up to f/5.6, I think you may have experienced sample variation, which we know from lensrentals data happens more than we realize.
Also, re your f/2.8 vs f/3.2 on Pentax, if an equivalently-sharp lens is really sharp at 12MP, it's sharp at 16MP or 24MP - the only way you would think it's softer is if you were pixel-peeping (or printing larger than before,) and then you're looking at a magnified image of the same performance, which isn't an accurate way to look at it. (think: a brutally sharp knife remains just as sharp if you look at it's blade edge with a magnifying glass, or a microscope. It doesn't look sharp at all in the microscope, though.)
At the same display sizes as before, a lens is going to look as sharp or sharper if you add megapixels, possibly even a bit more detailed/crisp if you're downsampling to get to those same display sizes.
Re the lens - fantastic optically, and a bargain at $750 or so.
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