[Leica] Erwin's explanation

[Michael Scarpitti <mikescarpitti@yahoo.com>]

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From: "Erwin Puts" <imxputs@knoware.nl>  | Block
address 
To: <kodachrome@kjsl.com> 
Date: Thu, 1 Jun 2000 20:25:30 +0200 
Subject: [Kodachrome] Some data to bring sanity to
this list again 
Reply-to: kodachrome@kjsl.com 
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Lenses for photographic systems are corrected
primarily for the spatial
frequency range of 5 to 20/30 lp/mm. And it is
wellknown that the 
10lp/mm
are instrumental in giving the psychological sharpness
impression.
As the MTF curves can be cascaded (multiplied with
each other), it 
makes
sense to look at the MFT data of films in the same
range.
Here are the figures for 5, 10 and 20lp/mm
K25: 115, 120, 100
K64: 110, 115, 95
K200: 110, 115, 95
E100VS:105, 100, 98 for blue light and 100, 85, 60 for
red light. This 
is
the first time that a manufacturer gives data for
different wavelengths 
and
that may be very significant. All other films also
respond differently 
to
different wavelengths.
Fuji Velvia: 110, 115, 100
Fuji Provia: 110, 110, 100

If I now take an excellent lens, like the Leica
Apo-Summicron-ASPH 
which has
100% for 5 lp/mm, 95% for 10 lp/mm and 90 lp/mm at
optimum aperture we 
get
these composite figures for K64:
100x115, 95 x 115  and 90 x 95 = 115, 109, 86
For Provia: 110, 105, 90
An excellent Canon lens (1.2/85) will give MTF data at
10 and 30 lp/mm 
(so I
have to interprete a bit here)
10lp= 95% and 20lp= 85%
Using Provia again: -, 105 and 81%.
Using K64: -, 109, 81%

Anyone wih a calculator can do his/her own sums. What
this tells you is
this: the percentage difference at the 20 lp is
significant between the
Canon and Leica lens.  It does also tell you that a
Provia film with 
this
Leica lens is as good as the Canon lens with K64.
Basing yourself on only these data leaves out many a
significant 
variable
and is detrimental to a real and serious assessment of
the parameters
involved.
Why is it that K-films do give more sharpness
impression and and 
improved
definition of finer detail. The K-films are grain
based, while the 
F-films
and generally all E-6 films are dye cloud based. A dye
cloud has 
smaller
area than a grain clump, because of inhibitors, but
also decreases the
acutance effect, which is then artificially
(chemically enhanced). 
Still
grain based films (like any B&W film) have beter
acutance and so will 
record
finer details till the grainines overcomes the detail
rendition.
The superiority of K-films is the combination of edge
sharpness 
(acutance),
its grain structure, its three layer (versus 16 layer)
and its high MTF
values. All in combination! You cannot single out one
elemenent and 
make a
case of it. The whole is more than the sum of the
parts.

I have no intention to be an evangelist and the case
for religious 
converts
is over since the middle ages (even if there is one
person thinks
otherwise). Outstanding imagery is possible with
Canon, Nikon, Leica 
etc and
E-6.
One caveat: the very fine qualities of K-films can be
appreciated if 
the
lens is accurately focused, expertly exposed and the
camera is 
vibration
free during the exposure. The acutance effect is
diminished when there 
is
movement blur involved.
In my view the qualities of K-films reside more in the
grain based, 
three
layer structure than is a carelees juggling of
figures. And a last 
warning:
not every Leica lens is on the Olympic hill. So the
statement that 
leica and
K-films are giving a special dimension to 35mm
photography has at least 
to
amended to the question which leica lens you use.
Agin sweeping generalisations are counter productive
to a purposeful
discourse of the merits of the K-films and how to
exploit their 
potential.


Erwin




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