Re: [Leica] NOCTILUX

[Erwin Puts <imxputs@knoware.nl>]

>The New York Leica photography I once owned had the U.S. introduction to
>the 1.0 lens. In that, they said they increased the contrast and lowered
>the resolution just a tiny bit because they figured that the lens would be
>used with high speed films. Thus they tiny loss of resolution would not be
>missed, and the significant increase in contrast that such a move would
>allow would make pictures "look" sharper because of the increase in
>performance in the kind of light the lens was intended for.
>
>So what is it?
>==========

Whatever salespersons say or have said, it is highly improbable that a
'tiny loss' of resolution gives a 'significant increase' in contrast. There
is of course a trade-off between contrast and resolution. The bargain
however is more even handed that these persons suggested. The Noctilux has
quite contrast and also lower resolution than the Summicron, so if a
tradeoff is necessary in the Noctilux it is evidently not needed in the
Summicron. The lower contrast of the Noctilux is caused by inherent flare
(large glass elements) and spherical aberration and some coma too. Within
its own optical parameters it is wise to opt for contrast more than for
resolution, but the real choice is for what spatial frequencies do we
optimise contrast.
To say it simply: the Noctilux has good contrast at f/1, but at f/1,4 the
contrast is lower than what the Summilux offers at f/1.4 and at f/2 the
Noctilux is still a bit below the contrast level of the Summicron at f/2.0.
*
It is by the way not true that an inherently low contrast lens would be
preferable in high contrast light situations. The rule that exists in
negative/print relations (low contrast neg necessitates high contrast
paper) does not hold in optics and light. The lens has no characteristic
curve, nor has the high contrast light situation. A high contrast subject
can have a 7 stop difference between deep dark objects and specular
highlights. A lens can artificially reduce this contrast if it has a high
flare level, to an overall contrast of 6 or 5 stops on the film. In such a
case the dark shadows get some veiling illumination from the flare level.
The highlights are not effected.
Nor is the micro contrast, responsable for the excellent separation of
small subject details.Here we need a high contrast lens that additionally
can handle fine details. As a typical high contrast scene has a lot of
shadow and  dark to midgrey tones, good separation is most welcome. And as
it also preferable to have separation of light grey and almost white tones,
a lens that can hold contrast in these highlights is a bonus. A low
contrast lens is quite often a flare prone lens and then all small details
in highlights and dark tones are washed out. Low contrast lenses exhibit a
tendency for high resolution which itself reduces contrast. So again, not a
wise choice in high contrast subjects.
Erwin