[Leica] MTF Data

[vintagepedaler at comcast.net (denik)]

An excellent source is Osterloh's Leica M The Advanced
School of Photography. pp53-63.
Another source I use for information is Image Clarity
High-Resolution Photography by J. Williams. Very technical
and way over my head in comprehending formulas.
I'm not a trained optical engineer but I read a lot about
all types lenses whenever I can.  With feedback on all
camera forums, one can guesstimate if a certain lens will suit
thier personal needs. And leave some muttering to themselves
"I wonder where the bokeh went when they added that
aspherical element"  when they sell their 20 year old lens
and purchase the newest SOTA lens design.

I've been following Leica posts for years about MTF's
& nothing ever mentioned that MTF's indicate how well
a lens holds contrast in the image. Some lenses are designed
to hold center sharpness & minimum peripheral & others
designed to give an overall balance with center sharpness
sacrificed to improve edge performance. Here's an example.
>From a family of curves ( 50 nocti, Summilux  & 'cron lenses)
you'll find the imaging quality of one lens is superior to
that of another at one aperture setting, but inferior at
different settings.

However just looking at MTF's is only a part of the lens
performance.
Simply, Modular Transfer Functions together with the Phase
Transfer Function (main characteristic to evaluate coma)
are parts of the Optical Transfer Function.
Note: MTF curves reveals nothing about color correction.

The answer of why M lenses gives more of a 3D image on the
negative is something we all have been wondering about.
To date, I have not found a hint of this in any Leica literature.
One can only hope this *fingerprint* is carried over to
the digital bodies. This should keep all of the weekend
workbench warriors busy thinking for the rest of the winter.

denik