[Leica] MTF, lens quality, photojournalism. filters

[Erwin Puts <imxputs@knoware.nl>]

MTF: why is the contrast transfer above 100% from 1 to 20 cycles/mm?
Some developerscan be designed to maximize what is called "adjacency
effect" or "heighbourhood effect". When a developer reacts on exposed
grains, the chemical reaction will be exhausted after some time. If we have
two areas, differently exposed (black and white as in the bar-line test),
the development reaction products diffuse from the high density side of the
edge to the region of lower density wher ethey restrain development and
produce a lighter zone called a fringe or Mackie line. The fringe and the
border are as it were artificially enhanced in density values (on the plus
and the minus side). The result is a blacker than black and a whiter than
white fringe on the edge. Measurement of the MT value than is higher,
relative to the uniform sensitometric contrast of the normal barline
values. This compensates for the normal light scattering of film and
optics.

Some luggers noted that many Leica users do not value the optical quality
of the Leica lenses as they do not need it (photojournalists in print)  or
do not care enough, as other qualities of Leica equipment loom larger.
There is a grain of truth in this remark. Indeed in print especially daily
or weekly papers most of the lens qualities cannot shine. Some do:flare
reduction, edge contrast, overall contrast, image quality in the field and
outer edges. Most newspictures are not made in circumstances where the
photographer can even think about the rules of optimum quality.  Still even
here Leica shows some advantages, however slender (disregarding mechanical
durability etc).
But generally I find it difficult to see a clear image quality advantage in
newsprint.
Some time ago there has been some praise for the 2,8/135. Well in fact this
lens is a weak one in the Leica stable. It is commendably good at recording
the overall outlines of objects and some fine detail is also decently
captured. In the field the performance drops rapidly. Now what is the snag:
do the users who praise this lens adhere to  different standards of
performance, do they not delve deep enough into the optical properties, are
they using emulsions that cover up for image defects, are they recording
objects that smooth away optical aberrations (as the comparison of Leica
and Canon showed) ?
OR: am I as a tester to far ahead into the computer prints, the 100 times
projection blow ups and the excessive focus on the finest possible textures
and image details. Could it be that Mulder and Scully need to take a blood
sample of me to see if I am infected with a Leica virus. ?
Kidding of course. In a serious vein: modern Leica lenses are exquisite
examples of the Solms wizardry. Did you know BTW that the 1.4/50 Summilux
- -R production samples have better MTF graphs than the theoretical
predictions: prove of a very refined mechanical production system and very
tightly hold tolerances.
Still: not all of us Leica users need this quality and I think we are wrong
if we would force everybody to standards they are not interested in.
A football coach in a  small town can be happier than a  Big league team coach.

So it is with filters: for one person simply anathema, for another one a
convenient instrument. Yes it degrades quality by about 5% (arguments
sake). But if you are on a 50% level of maximum quality what the heck? To
give some relativism: if you need to go to the diffraction limit with some
Leica lenses a filter is necessary: to cut out some wave lengths that play
havoc with aberrations. Is the resulting image better or worse?

The only way to advance the Leica base knowledge is to think, research and
argue. Not to repeat what we heard somewhere.

Erwin