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03-25-2010, 03:15 AM   #31
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QuoteOriginally posted by falconeye Quote
Yeah, there are rules of thumb how softness increases due to air turbulence (A) and dust (B). I forgot the exact rules but a 300mm is often beyond this limit already.
When I first got that K 500/4.5 I did a lot of trials to get a feeling for the sharpness and contrast I could expect. I was very disappointed and even disassembled the whole focusing assembly and rebuild it with a slight modification, to get the focus beyond infinity, as I never was able to get a sharp shot.

Then I made comparisson shots with my medium format Meyer-Optik 500/5.6 and saw, that this lens (which I know to be sharp), deleivered nothing better. Than it finally dawned on me, that testing infinity focus during summer wans't a good idea with such a long focal length. The air was way too turbulent and slightly hazy, rendering all trials invalid...

I have since used the lens in calm, much less turbulent, winter conditions and it turned out as sharp as I had hoped for and had seen at shorter distances... Atmospheric seeing shouldn't be underestimated, when people complain about the lack of sharpness of their lenses!

Ben

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