[Leica] Myth and anti-myth

[imx <imxputs@knoware.nl>]

It is remarkable that the idea that there is a significant trade-off between
high contrast and low resolution still rides high in Leica lore. As far as I
know no one who holds his view has ever presented demonstrable evidence or
corroboratable measurements to prove this point. Generally a high contrast
implies a high resolution and the other way around. It may be that a shift
in focus plane may change this relationship to a small degree, but the
general correlation is evident. More contrast is higher resolution. And
statements to the effect that a "slight" reduction of contrast brings a
"slight' improvement of resolution beg, nay scream for evidence.

Now to kill two more myths. Sometimes I feel like Buffy the Vampire Killer.
I have the Kodachrome films which I used as comparison for the 100 to 400ISO
slide film test some weeks ago. Results will kill some preconceived ideas.
The King of all slide films is by now the Kodachrome 64, which resolves
easily 90 lp/mm, much more than the E100SW and even close to the resolution
of TP in normal circumstances. Especially noteworthy is the excellent
acutance, the great clarity of detail and the fine grain. A disappointment
was the K25 which at best was as good as the K64, with a small gain in grain
smallness, but not enough to offset the drop in speed. The fading out of the
K25 then is sensible. No added value. Sorry.
Big surprise the K200, which showed as expected a tight but visible grain
pattern, but a resolution that beats the Provia 400F at 70 to 75 lp/mm. So
the idea that fine grain supports high resolution is as false as the idea
that low contrasr supports resolution.
If you want to test the qulaity of your lenses, there is only one easy way:
use K64! and even K200 will show the defects of most lenses. Do some actual
testing!

I also had the opportunity to test the surfaces of filters on an
interferometer. Results will kill another myth. I used four different BW
filters in several colours (not relevant for testing, but to show that there
must be different batches).
Results? Take a deep breath: NO, absolutely NO image degradation by the
filter as all surfaces of the four filters were absolutely plane to the
highest possible degree. At worst only one interferometer stripe for the
experts. 
Of course secondary reflections are possible. But the commonly held notion
that the addition of the filter adds two surfaces and by that fact should
degrade the image quality is simply not supported by measurements.
A well made filter in front of the lens will NOT make a drop of image
quality!

These results show that myths are fine if you wish to cling to stories that
seem sensible because they are repeated over and over again and even have
been 'explained' to some degree. But so the flatness of the earth had its
followers and scientifically based stories. But only measurements bring the
facts. 

Erwin