Re: [Leica] MTF analysis

[Erwin Puts <imxputs@knoware.nl>]

>After having read the arguments against the mtf test of Leica lenses,
>especially those developed by Erwin, I must conclude that MTF is not
>objective because one test is inadequate and because a lot of measures
>needs a subjective interpretation.
>Well, as it is the general case in science, I must conclude that science is
>inadequate or subjective.I think this great post modern discovery deserves
>a  name. I propose : the LUG impossibility hypothesis.
>

Dominique,
I am afraid you have completely misunderstood my reasoning and arguments.
Undoubtedly it is my poor English that forced you to the conclusions noted
above.
Let me restate.
One: I am a great admirer of MTF graphs. I do think they give invaluable
information about a lens performance and MTF measurements are as objective
as can be produced in this scientific world. I am not "against the mtf test
of Leica lenses" as you infer from my postings. I really never said that
and I would like to set the record straight. I only noted the way CdI
interpretes the mtf numbers: weighting them and attaching to the resulting
numbers a description like 'very good'. I also do seriously question this
type of presentation. The presentation is subjective, not the mtf numbers.
Two: Eric is partly correct in stating that any MTF graph on its own and
isolated  from other info, easily generates half-truths. The mtf values
correlate surprisingly well to the sharpness impression of a picture.
Third: the mtf graph does not give any information about colour rendition,
close-up performance, light falloff,flare suppression when strong lights
are shining in the lens, gradation of subtle hues in fine image details
etc. Therefore the mtf info is usefull and objective, but not conclusive.
Fourth: the evaluation of a lens is indeed a creative act, based on as many
objective figures as possible (including mtf graphs), but in the last
analysis the evaluation of a performance of a lens is *like it or not* a
subjective act.
Compare it to the way a literary expert would analyse a poem. You can
collect any number of figures about the use of words,the relation between
concepts, use any semantic or syntactic computer analysis program. In the
end the beauty and impact of a poem can not be quantified to the last
punctuation. So it is with a lens: a lens has character and a certain
balance between many optical parameters. This balance gives the lens an
ability to record the world in front of the camera with a certain
fingerprint, different from other designs. This is what we like about Leica
lenses, even if on some measurement the score is lower that that of the
competition.
Fifth: I do support the free press, but the press has also its
responsabilities to steer away from easy conclusions and possible
mis-interpreations. Here I can admire the position of the most respected
British Journal of Photography, that steadfastedly refuses to print mtf
graphs, as they are so easily misunderstood without a thorough optical
background. They prefer to describe a lens in words any photographer can
understand and relarte to the photographic practice.

Erwin