Thou dost fret too much. You forgot to read the most important part of
Roger's message:
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What Does It Mean in the Real World?
Like a lot of laboratory testing, probably not a lot. Adapters couldn't
all stink or people wouldn't use them. Like a lot of tests, you can
detect a very real difference in the lab that doesn't make much
difference at all in the real world.
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ps: Even 50 lines/mm resolution (let alone 80) is very difficult to
achieve unless you're on a rock solid tripod.
Dr. Focus
On 3/16/2015 8:05 PM, Mike Gordon via olympus wrote:
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 ta
ngential 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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