[Leica] Laney, lens testing and 3-D effects (long: this is not Hubert)

[Erwin Puts <imxputs@knoware.nl>]

Recently a very interesting discussion has been launched about the
difference in characteristics between actual and earlier generations of
Leica lenses,
Some of these differences are undoubtedly real. I have pointed them out
frequently  and a year ago we had a similar exchange of opinions between
Alf (who very regrettedly left us) and myself. Alf valued the
characteristics of the older lenses for many reasons.
And I would not in the least question his opinion or choice.
We have to be very careful  around this topic.
To like some characteristics is not the same as stating that these
characteristics are virtues or to imply that they are desirable in
themselves.
The discussion now is focused on a perceived change in Leica design
philosophy as exemplified by  statements from Osterloh and Laney.
The core argument seems to revolve around Laney's statemant that "They
started from the proposition that the subjects we photograph very rarely
consist of grids of black and white lines on flat sheets of cards."  The
corollary is that one can design lenses to do very well on standard test
subjects and lenses that are designed for real life subjects. These latter
designs invariably (by design and subject matter) perform poorly on
standard test subjects.
First of all: this argument is one big fallacy. Every lensdesigner and
every lens ever designed is designed for real life subjects. The only
exception might be special reproduction lenses where flatness of field is
of utmost importance. All lens designers assume in their design that we
have in front of the lens an object in three dimensional space. As this
object has to be recorded on a flat plane (the emulsion) and because of
light rays behaving a bit weird when eased through an optical system of
several glass elements, we encounter aberrations. (More about this in my
Viewfinder article next issue). These aberrations have to be corrected and
balanced. This is the task of the designer and he can do this with more or
less creativity and expertise. There do not even exist any design rules or
computer programs that are tuned to twodimensional objects as black and
white barlines.
Furthermore: Zeiss engineer Mr Hanson introduced in 1943!! the notion of
contrast (what later became MTF)  and its exact correlation between optical
quality and human sharpness perception. And Zeiss have always followed that
lead. I would not be surprised if the 'defensive line' of Leitz/Leica in
the past has a lot to do with the image quality of Zeiss lenses.
We have two types of testing equipment. One group that checks for
production tolerances and are used in factories to assure prescribed
tolerances. The second group is designed to test lenses for their
capabilities in recording real life objects. Be it a barline test, an MTG
graph or a beautiful girl, each one tries to find out the characteristics
of the lens in question for recording 3-D objects.
It is BTW remarkable that the Elmarit-M 2.8/28 (fourth generation) has been
referred to as the last lens of the great old generation, while it in fact
is one of the first of the NEW generation. Perception is a very quirky
business.
Also the notion that modern Leica lenses move too far in the direction of
high  resolution and therefore lose many of their former unique
characteristics is not substantiated in practice. Yes modern Leica lense
have a superb clarity of very fine image detail, a stunning repression of
veiling glare and a very high correction of spherical aberration and many
lateral chromatic aberrations, all characteristics that give 3-D objects a
very faithful rendering in a flat plane. As a fact when comparing real life
pictures (not barlines) taken with the old and new Summilux-M 1,4/35 (asph
and non-asph) any viewer, not just me commented on the sparkling lifelike
representation of the asph version.
Let us not try to create false dichotomies where none exists.
Specimen of older Leica lens-generations are very good and sometimes
surprisingly competent lenses. And one should admire the perseverence and
competence of the designers of these lenses. Newer generations incorporate
more research and more knowledge about the way an on object in space should
be recorded as an image on film.
The Noctilux does not perform poorly on any testobject (girls or barlines
or MTF graphs). It performs quite good on all test objects. If a tester
would note that the Noctilux has less contrast and whatever else he would
like to mention than a Summicron he is correct. If he would conclude that
it is therefore a bad lens, he only  proves his own incompetence. A  lens
with the specs of a Noctilux cannot ever produce the image quality of the
Summicron. No tester can use one yardstick and evaluate all lenses in a
onedimensional way.
Laney refers to a socalled ' edge spread width criterion' and some Luggers
now infer that this a criterion that favours older lenses while asph
versions can cope better with normal test targets.
Let me be quick and mercifully: this 'edge spread width criterion' does not
exist. We have the point spread function, and the linespread function and
we have the acutance measurement. What Laney does is copying the contents
of  a research paper that is just that: a research paper. An "Ansatz" as
the Germans would say that never was followed up and went the way many
research papers do: they evaporate.

Erwin