EXCERPT page containing first few paragraphs. 2019-03-24 15:18:50
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Brand-new blur is not confined to any brand or price level.
A slight defocus can help reveal lens problems that are otherwise muted by depth of field; if a lens has asymmetry: a slight defocus can make one side sharp and the other blurred. Alternately, a non-planar subject such as a gently upward-sloping hillside with generally similar subject matter can show a cut of sharpness that is skewed forward on one side.
As shown below, a brand-new Leica 180mm f/3.5 APO-Elmar-S had asymmetric sharpness. Several tests all confirmed the same problem. A 2nd sample of the 180/3.5 was not available, so a camera lens mount to sensor misalignment cannot be ruled out. However, no asymmetry was seen with the the 70mm f/2.5 Summarit-S ASPH on the same scene on the same camera body, and camera misalignment is generally more noticeable with a shorter focal length.
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These systems are hugely expensive, so make the right choice for your own needs (full frame vs medium format).
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