[Leica] MTF analysis

[Erwin Puts <imxputs@knoware.nl>]

Dominique wrote:
>You write :"The straight results from the machine are as usual completely
>reworked to become meaningless".

>They write :
>"MTF is measured 0, 3, 6, 9, 12, 15, 18, and 21 mm from the image center
>(on axis), at 10, 20 and 40 lp/mm, in two different directions (sagital and
>tangential). That is all together 48 measurements at each focal length and
>each f-stop. Rather than listing all these numbers we calculate a weighted
>average number for each f-stop of all lenses and each focal length of zoom
>lenses. The center of the image is more important than the edges, and 10
>lp/mm is more important than 20 and 40".

>That's a fair statement of the methodology we can discuss about.For
>instance : why 10 and not 20 or 40 lp/mm ? What are the weighting
>parameters ? But we can't gun down in two shakes the work they publish as
>you do.
 >
>Moreover the graphics (without weighting parameters)are like the Leica's
>ones...

I did not and do not question the raw measurements by H'blad and CdI and
Photodo. The Ealing is a well known instrument and yes Leica uses one too.
The measurements on and off center (0 to 21mm), the lp/mm and the
tangential and sagital orientations are the classic ones pioneered by Zeiss
and used by all others. These raw data are only interpretable by trained
people and the produced data are very sensitive to the one using the
machine.
Using the weighted figures is not a good method. I know, because I have the
calculations, that Photodo gives a very strong weighting to the performance
at f/8 (presumably to give zooms a fair chance), in combination with the
center and the 10 lp/mm. This combination takes most of the weighting and
therefore  the results are as I stated meaningless. I am not gunning down
in two shakes anybodies work. I just happen to know more than you assume.
I have repeatedly stated that at f/5,6 in the center and for the contrast
of object outlines ANY lens in the world will produce decent results. Thats
exactly what photodo is measuring and evaluating.
They give a very low weighting to in the field performance, the 40 lp/mm
and the full aperture: this is precisely the area where Leica can score and
excells. So their weighting for us Leica users is very uninformative.
That is what I said and I see no reason to retract this statement. In fact
I feel even more convinced by their public statement (which I already knew
as I was partially involved in their weighting strategy) that  I am on the
right track.
I strongly opposed to their weighting as it is not relevant tp modern
optical practice, but my voice (as usual) was overruled. I do presume that
my weighting would disadavantage some manufactures and products.

Erwin