I consider this all a bunch of "doesn't affect me at all". In the first
set of tests linked below there is no mention at all of aperture. My
conclusion is that all tests were performed wide open. He then goes on
to say (unlike portrait photographers concerned about center
performance) that landscape photographers might notice the edge
performance degradation discovered in the test. But how many of you
landscape photographers use f/2 or f/1.4 lenses wide open? Certainly
not me. Then CH Ling pointed out (using tests of Leica lenses) that
even these lenses have significant field curvature wide open. Tilting
the lens would potentially minimize or exaggerate the curvature from
side to side... but it's still just tilting the lens by a very tiny amount.
Then we come to the second link which says: Hey! Wait a minute. My
tests of last year show bad results because I didn't account for digital
filter stack thickness in the tests because we were using the optical
bench and not camera bodies. When he inserted an appropriate clear
glass filter of the thickness the lens was designed for everything got
much better.
My conclusion from all that it that much of the problem he originally
attributed to adapters was actually due to his testing method. It also
points out that our old OM lenses weren't designed for use with a 4mm
thick (m.4/3 size) piece of optical glass in the optical path. But we
are only using the center of the image circle. Perhaps some lenses
(wider ones probably) will not fare well as adapted lenses. But
everything I've tested performs at least as well as I need it to.
My $10 m.4/3 adapters work just fine for what I want them to do. Case
closed.
Chuck Norcutt
On 9/26/2014 6:43 PM, Mike Gordon via olympus wrote:
Parallel Puzzle Moose writes:
<<<I don't now recall if the issue was parallelism, length, ??, but the
<<<same logic applies. And yet he had careful test images showing a
<<<difference between adapters. Absent another theory, one is forced to
<<consider that very fine machining differences may matter. The
<<<differences were minor, and only visible in A-B comparisons at 100%, but
<<<certainly there.
Adapting lenses can be a bit tricky to get optimum results. Why adapter
issues withWA lenses with corner issues seems to be a predominant
complaint is not clear to me. I recall believable posted images by the
pixel peeping alt lensers on FM. Some sensors seem more subject to
corner smearing/color shifts with more divergent rays as well in lenses
designed for different platforms. Sensor stack thickness can play a role
in degrading expected performance as well especailly in morrorless cams
with thick senosr stacks.
Ming Thein seems to think the adapter issue is more cricial on short
registartion mirrorless cams but I don't remember any rigorous
supporting data.
Roger at Lensrentals is really good at teasing out the issues:
http://www.lensrentals.com/blog/2013/09/there-is-no-free-lunch-episode-763-lens-adapters
http://www.lensrentals.com/blog/2014/06/the-glass-in-the-path-sensor-stacks-and-adapted-lenses
The varation in performance with adapters was much greater than typical
sample variation with good lenses.
Adapt often but with caution, Mike
--
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