AG writes:
The fact is that whatever is in focus is going to be more in focus
with a heavily corrected lens assembly whether aspherical elements
are
used or not.
Yes, very highy corrected, (some would label overcorrected for
spherical aberation lenses produce funky bokeh whether they have
apsheric elements or not--witness the excellent OM Z 50/3.5 with macro
shots and a distant background. See the Dr. Nasse article again. In
many respects it is a zero sum game.
http://www.smt.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_35_Bokeh_EN/$File/CLN35_Bokeh_en.pdf
If one optimizes for nice background bokeh , the foreground bokeh can
get very busy and if spherical aberrations are too highly corrected
lots of stuff happens including increased bright rings around the OOF
bokeh highlights--to quote Nasse:
"....stronger counteractive measures towards spherical overcorrection
strongly increase the brightness around the circumference of the
circles of confusion:"
Now larger formats have a distinct advantage as the degree of
blurriness in a distant background is a direct function of the physical
size of the aperture. All that be said bokeh variables are highly
complex and very dependent on the aperture, relative
foreground/subject/background distances----is mentioned by Nasse as
well.
I seem to agree with AG that apsheric elements do affect the drawing
style or "rendering" of lenses but I'll defer to him on the reasons.
I recall Roger Cicala of Lensrentals has proposed ,----- 'render' is
usually what lenses do when they do nothing else particularly well.
A bit harsh, I think.
Mike
--
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