I am very comfortable carrying my OM bodies and Canyon digital back but prefer
to lug less heavy stuff these days.
Thus my toe dip into MFT and possibly sony in the near future. I really like
the new high performing lenses these days
but miss some "rendering character" of my lenses built for film. Many newer
ones are very sharp inded but tend to have
a sameness about them and fair to middling bokeh---this is a vast
generallization with some glaring exceptions. Perhaps the aspheric elements
play a role. Anyway I enjoy the character and adapting of my old friends.
I do not have a good handle on the complexities of determing how to achieve
optimal performance. The adpater quality/precise dimensions seems to one
variable. (Expense did not guarantee a good match for a lens in Roger's tests
at lensrental)
http://www.lensrentals.com/blog/2013/09/there-is-no-free-lunch-episode-763-lens-adapters
This is not a trivial issue for wide angles and seems to be especially
importnat for those with floating elements (may interact with sensor stack
thickness) Minor offsets in thickness effect the peripheral rays in a nonlinear
way and not corrected by depth of focus considerations. The corners just become
lousy. Some lenses seem to developefield curavture. While the inherent
amount of curvature in the optic will certainly vary from lens to lens, moving
a given lens forward or rearward will have a non-linear (curvature is
non-linear) relationship change between the distance to the center of the film
plane vs. the distance to the corner. Shimming the adapter to get infiinty
spot on corrects this. I don't understand this fully. Dr. Focus was
skeptical of any serious issue.
Another issue is the stack thickness already discussed and posted previously.
http://www.lensrentals.com/blog/2015/01/a-thinner-sensor-stack
There is now a commercial correction for this!! Some WA's as long as 28mm are
affected.
http://www.kolarivision.com/thinfilterconversion.html
From Dr. Nasse at Zeiss--mostly an issue on tangential plane:
From Nasse:
"Lenses with a very large beam tilt react in a much more sensitive manner to a
change of refractive index in the image space caused by filter plates in front
of the sensor (such as low pass and IR-blocking filters). If the filter plate
is not considered in the design of the lens, the edge definition will suffer.
The effect of the additional path through the glass grows exponentially with
the beam inclination. A Distagon which never achieves more than 20° beam tilt
in the corner of the image reacts more tolerantly than a symmetrical wide-
angle lens, which might reach a 45° tilt. This is why filters in digital Leicas
are very thin – to remain compatible with older optics. If the filter is
significantly thicker, the contrast transfer for the image edge becomes worse
for tangential structures. In the graph of the curves, this looks like the old
retrofocus lenses but is caused by astigmatism rather than lateral chromatic
aberration. The focus is shifted to greater distances for tangential structures
by the additional path through the glass. If the best edge definition is to be
achieved, then all that can be done is to stop down further."
I wish I had a good handle on these issues.
Adaptation bewilderment, Mike
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