Hello,
I'm not sure if this was already discussed with previous discussions about
bokeh, but the Japanese photographer Toshihiko Oka describes some lenses on
his homepage ( http://www.page.sannet.ne.jp/tsoka/pentacon_e.html ). Many
lenses have, as he says, a "dual lined blurred phase" because of (spherical
?) over-correction. The Xenotar is according to him an example of a perfect
corrected lens without such a dual lined blurred phase. I'm not absolutely
sure, what he means exactly, but if you take some lenses, like the Zuiko
macro 50mm 1:3,5, and look at your finger tip as if the lens is a loupe,
you can often see between the (brighter) finger and the (darker and
unsharp) background a "blurred phase" with a different brightness than both
the finger and the background have. This can seem like an edge (and so
contrast) enhancing effect (similar to sharpen in digital picture altering
or the physiological edge enhancement by the retina). Other lenses don't
show this effect. So maybe the Zuiko macro 50mm 1:3,5 indroduces an edge
enhancement because of (spherical ?) over-correction. This would be an
explanation, why this stunning effect is not found with modern very best
lenses, because they are perfect corrected like the Xenotar. Just an idea
of mine.
Matthias
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