R: [Leica] an objective evaluation of leica M lenses??

["Guido Ridoli" <guirid@numerica.it>]

Thanks Erwin for the perfect reply
You are great

...PROFITABLE to someone IS TO READ LESS BOOKS AND SHOT MORE
ROLLS...
+ADs--)

      Guido Ridoli
  LEICA M superfan
  guirid+AEA-numerica.it

- -----Messaggio originale-----
Da: Erwin Puts +ADw-imxputs+AEA-knoware.nl+AD4-
A: leica-users+AEA-mejac.palo-alto.ca.us
+ADw-leica-users+AEA-mejac.palo-alto.ca.us+AD4-
Data: luned+AOw- 20 aprile 1998 16.46
Oggetto: Re: +AFs-Leica+AF0- an objective evaluation of leica M
lenses??


+AHw-
+AHwAPg-The evaluation of the Noctilux made by the french review
+ACI-Chasseur
+AHwAPg-d'images+ACI- is objective, i.e made with the MTF
analysis.Leica Camera does
+AHwAPg-the same and publishes some of the results (not for the
Noctilux, of course
+AHwAPgAh-It's too bad+ACE-)
+AHw-
+AHw-First of all: Leica's policy is this: they do not publish
MTF graphs of
+AHw-older lenses in general and not because of bad results. You
will not find
+AHw-published MTF graphs for the Summicron-M 50 and the
Summilux 75, themselves
+AHw-star performers in the current Leica line-up.
+AHw-
+AHw-The MTF measurements of Leica are totally different from
the ones of CdI
+AHw-and for that matter: both differ from Zeiss. The reports by
CdI cannot be
+AHw-objective. What happens is this: MTF measurements are made
at several
+AHw-spatial frequencies and the contrast figures in exact
numbers are graphed
+AHw-over the image field. So we can say that at an image point
6 mm from center
+AHw-the 10lp/mm are recorded with 90+ACU- contrast transfer. At
40lp/mm the same
+AHw-point reaches 40+ACU- in the tangential direction and 35+ACU- in
the sagittal
+AHw-direction. This information is objective (but no longer
interpretable by
+AHw-most persons).
+AHw-Now what does CdI do: they produce a weighted average of
these figures (the
+AHw-weightings are unknown to me, but maybe Dominique knows).
And this weighted
+AHw-result is attached to a word, like fair or very good. Here
CdI assumes a
+AHw-linearity that does not exist.
+AHw-I do know of a Swedish  magazine that also uses MTF figures
(from
+AHw-Hasselblad). They put the figures (very accurately) into a
spreadsheet and
+AHw-manipulate the numbers to get a condensed figure or word.
Their weighting
+AHw-and numberjuggling  favors the performance at f/8 in the
center. Hardly a
+AHw-noteworthy exercise.
+AHw-As far as the Noct goes: the results at full aperture for
the 40lp/mm must
+AHw-be approached with some background knowledge (read my
report in
+AHw-PhotoTechniques soon). The quality at the 10lp/mm however
offsets the
+AHw-results at 40lp/mm and the Noct adds its own special
characteristics
+AHw-(excellent rendition of fine textural detail, which at
f/1.0 is much more
+AHw-important than the ultimate in resolution).
+AHw-The defects of the CdI method are quite clear: They use one
set of
+AHw-calculations to generate one overall qualification. This
calculation
+AHw-however is only one of many possible weightings and without
the actual
+AHw-weighting and explanation of their choices, we have the
famous case that it
+AHw-is easy with statistics to prove anything you want. CdI
themselves note in
+AHw-their explanatory article that wide apertures strongly
influence negatively
+AHw-the overall score because of their weighting in the overall
calculation.
+AHw-They use the spatial frequencies of 10, 20 and 50 lp/mm and
even pick up
+AHw-100 lp/mm. Now 100lp/mm is so far removed from realism that
using these
+AHw-results would be quite dangerous. But even 50lp/mm is a bit
on the wild
+AHw-side. They also neglect the 5lp/mm that most commentators
regard as very
+AHw-important for overall sharpness impression.
+AHw-
+AHw-Erwin
+AHw-
+AHw-
+AHw-