Re: [Leica] image evaluation criteria

[tedgrant@islandnet.com (Ted Grant)]

Erwin Puts wrote:
I wont repeat it, you've all read it. And if you haven't, get your eye
balls glued to the screen and do so! :)

A wonderful lens lesson for all of us. Erwin, a great way to end the year
and thanks for making it understandable, even for us "working
photographers.":)

Wishing you a very healthy and Happy New Year, looking forward to more of
your  reports in '99.
ted



>My brother Hubert is a conservative and a pragmatic. He does not believe that
>progress is real and he cannot imagine that anything written since 1970 has
>any value. He also refuses to consider facts or logical reasoning that
>contradicts what he believes is true. But he is deeply involved in modern
>gadgetry (that is pragmatism). He uses these instruments as he pleases,
>whatever the intention of the designer might have been. He correctly justifies
>his approach with two arguments: it is my money and I like what I like.
>He constantly urges me to stop trying to update conventional wisdom in
>photographic lore to a level required by the actual state of the art of
>photographic and optical sciences.
>Follow the mainstream, he pleads, then your life is easy. Repeat sales reps,
>marketing brochures and every snippet of Leica lore that is floating around in
>this info-soaked world. He made these remarks after my recent visit to Solms
>and Oberkochen, where I was inundated by MTF graphs, spotdiagrams, ray fans
>and a plethora of optical aberrations that need to be corrected in a  very
>subtle and artistic way in order for us mortals to start raving  about Leica
>lenses.
>It took me three full years of testing and thousands of pictures (yes real
>pictures of real life subjects) to come to grips with the M-line of Leica
>optics. Now the daunting and very exciting task is to engage my self in the
>R-line. Another three years? Hubert tells me to use my spare time for more
>pleasant activities as studying the theoretical base of Startrek physics.
>Why am I giving my fellow luggers a peek into my family disputes? Well as
>Clinton becomes more popular the more dirty he talks and acts, I think we are
>at an intellectual and moral low point in history. Is there a chance that the
>classical Greek ideals of beauty, rational discourse and lust for truth will
>survive? At least in Startrek I presume. I am very pleased that Data has a cat
>(or the other way: the cat has Data). If ever a creature has the basic
>characteristics of a Leica M camera, it is the cat. This species survives in
>even the harshest and unfriendly environments, it never loses its character,
>it does not compromise,it is the most effective small predator in evolution
>and it is a thing of beauty. And above all: you can study it for years and not
>know anything about it. It still is a mystery, but a very nice one.
>These thoughts have been inspired by the recent discussion around that most
>elusive of topics: image sharpness. This topic pops up quite often and then
>fades out without any real progress. Still the topic is of utmost importance.
>So let me try to make some observations. Sharpness does not exist in any
>objective way. It is a subjective impression of the eye/brain mechanism and
>cannot be measured or defined. Note that I in my reports never use this ord
>'sharpness'. I use the optically correct words 'contrast of fine detail' and
>'edge contrast' to describe image chracteristics. Generally we may surmise
>both words under the umbrella word "clarity".
>
>When a designer creates an optical system, he/she has always a clear purpose
>in mind about what the lens has to accomplish imagewise. As any lens is always
>a compromise between many demands and variables, the resulting imaging
>characteristics can be related to the ideal lens: that is a lens without any
>defect, that will reproduce the object in front of the lens with 100%
>faithfullness in three dimensions. Let us make very clear that Leica designers
>NEVER assume that their lenses should or could be optimized for flat two
>dimensional test targets of whatever configuration. It is an undeniable fact
>that any real lens has only one, I repeat only one plane of accurate focus.
>That is by definition a plane of very thin depth. Thus evaluating a lens in
>the optical sense of the word is studying the characteristics of image points
>as they are projected on this plane of focus. It so happens that the MTF
>graphs are a very good analytical tool for just this: studying the point
>characteristics in the image plane.
>It is far beyond the truth to imply that a study of the flat image plane (that
>is what designers and serious testers do)disregards the three dimensionality
>of real life objects. To imply as some postings do, that a test of a flat
>object is irrelevant to practical photography, is to misunderstand the
>fundamental laws of optics.  There are many methods, some very complex, some
>very secret to make sure that the image characteristics that are defined in
>the plane of accurate focus can be extended to a three dimensional area, part
>of which is contrained by the angle of view of the lens and part of with is
>constrained by the depth of field of the aperture used.
>We have to make some distinctions: some tests that are proposed in common
>practice: photographing a newspaper page, photographing one of many testcharts
>(bar lines in many configurations) are not very meaningfull. This is not the
>fault of its inherent two dimensonality, but because the target as such is not
>very well correlated to actual imaging chararteristics of a lens. In the case
>of  standardized test patterns, we have the problem that most if not all users
>lack the necessary background to interpret what they see or think to see.
>Again we should not ridicule a methodology because it is falsely used.
>
>An expert designer can predict with a high level of accuracy how a lens will
>perform, just by looking at all his/her figures churned out by the computer.
>We should really bring ourselves to a higher level of awareness that the
>twodimensional test target versus three dimensional reality confrontation is
>not a meaningfull  distinction. We have bad tests and good tests and bad
>testers and good testers.
>
>Now the issue of evaluation. Many postings assume that testing a lens in any
>objective way (that is using tests that produce contrast or resolution
>data)has no relevance to the demands and requirements of working
>photographers. First of all I hope to have made clear that measurement of
>image performance is MUCH more than looking at 'sharpness' (which is a
>non-issue as it is not existing). A responsable designer and his companion the
>tester will choose very carefully those measurable characteristics that are
>very relevant to the image as required by working photographers. To assume
>that testers are otherwordly and/or insensitive  of the needs of real
>photographers is doing them injustice. Again we have good and bad.....
>
>There does not exist any evaluation method that can handle in one merit figure
>all the many characteristics of a lens.  And here indeed the acceptance of the
>working photographer is the last word. The role of the tester is to bring in
>figures based on carefully conducted tests to support or inform the user of he
>validity of his final decision. Or to help him make a meaningfull choice.
>
>There is no us-them situation. A tester might be a very good photographer
>himherself and a working photographer can be a lousy tester. It is the role of
>a tester (at least that is the way I see and practice it)to inform a working
>photographer of the potential image qualities of a lens based on scientific
>testing of, yes, two AND three dimensional objects. If a working potographer
>likes or needs or is interested in these characteristics is purely his
>nondebatable choice.  The image qualities I try to investigate are very
>relevant to practical phtography. Again: some of my test objects are indeed
>the barline patterns of a flat plane. If you really know how to translate
>these results into the demands of photographing cats and girls and snow storms
>and emotions, then there is nothing wrong with this method.
>
>Have a very happy new year where at last we can do what we need to do: use the
>imaging capabilities of Leica lenses to start recording the beginnings of  the
>third millennium in its myriad ways.
>
>Erwin

Ted Grant
This is Our Work. The Legacy of Sir William Osler.
http://www.islandnet.com/~tedgrant