EXCERPT page containing first few paragraphs. 2021-12-04 03:57:37
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Even the very best lenses can show asymmetries and these can change with minor focus differences: as elements rotate with focusing (or zooming), maintaining perfect symmetry is an elusive goal and perfection is likely reserved for cine lenses.
Very few lenses can achieve perfection on such a test and sample variation makes any conclusion about a lens design inappropriate. All that can really be said is that a particular examples has this or that weakness (at this or that focal length and focusing distance).
See for example, the Leica 180mm f/3.5 APO-Elmar-S cxample, noting that is is a expensive high-end prime lens with an asymmetry. If such lenses have symmetry weaknesses, how can we expect a varifocal lens costing half as much to be perfect?
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