[Leica] lens performance criteria (long)

[Erwin Puts <imxputs@knoware.nl>]

Alan wrote:
>I would like Erwin's opinion on what I write here, of course:
>1.Flare: flare is a pretty well corrected problem since a very long time on
>all 'classical' prime lens constructions......Just and example of the need to
>avoid generalizations.

I fully agree with this last statement. Sweeping generalisations most often
do more harm than good.
Flare however is a word with many meanings. We have 'veiling flare': which
essentailly operates as a contrast reduction factor as it is non-image
forming light and we have 'ghost-images' (reflections of light sources
scattered through the lens surfaces. The last ones are easily observed and
easy to generate. For image quality the veiling glare is the most important
and here I may say generally modern Leica lenses have an edge. It gives the
Leica images more clarity and transparancy. The ghost images are a
different problem. Some Leica lenses are very good (Noctilux). some are
only so-so.


>2. Tonal modulation: is this measured ? I find this is one of the less
>'measurable' opinions: the emulsion and the enlargement ratio are more
>important factors here than the lens. Erwin: would you argue that Leica
>lenses, as a range, have superior tonal modulation than the competition ?

I do not know of any optical parameter that equates with this "tonal
modulation".
I am aware of Transfer Modulation Function  which is an optical concept and
of tonal reproduction which is an emulsion concept. So the question if
Leica lenses are (not) better than the competition has a void answer. As
far as a filmemulsion can reproduce fine tonal differences, Leica lenses
can certainly deliver. But because of excellent veiling flare reduction and
high colour correction and excellent micro contrast.
Lenses do not have the property of tonal modulation.


>3. Color "bias": this would only be noticeable and relevant on slides of
>course. So, what is exactly the colour bias of Leica lenses ? Do you mean
>it is "warm" ? Thus not "true" ? Do you mean it is "neutral" and that the
>competitors are not "true" ? Anyway, if such a bias does exist across the
>line (this sounds possible because the coating technique is the same across
>the line), it would be a matter of taste rather than 'performance'. I do
>not trace color 'bias' on my Velvia Leica M pictures compared to my Velvia
>Nikon pictures: I enjoy (sometimes too) vibrant colours in both..

No lens can reproduce all colours of the visual spectrum exactly. Leica
lenses are mostly neutral, meaning  that the Macbeth colour patches
measured colorimetrically show little colour shift. As this topic is very
complex theoretically and also very prone to subjective impressions I will
comment on this one later.

>4. Contrast: this is one of the more obscure concepts in my eyes, depending
>on where you analyse it. I would find 'lens contrast' to be a measurable
>complement to "sharpness" and just as exacting to maximise in "normal
>shooting condition": this is a heavy tripod, ISO 25, f5.6 thing again. I
>might be wrong and would certainly like to read Erwin on this. Other usages
>of the 'contrast' concept make it a cousin of tonal range, more related to
>the emulsion/paper/scanner side of things. But I do often find a little
>more 'punch' in my Leica M slides compared to what I used before. Just
>cannot define that "punch".

Just as flare has different meanings, so does 'contrast'. Optically
contrast and sharpness are the same as you correctly presume.
Emulsion wise you are correct again as the Contrast Index defines the tonal
range. See my remarks above.
Contrast/sharpness is the most important influence on how we perceive and
evaluate a photograph. This characteristic is pushed to olympic heights in
modern Leica lenses and instrumental for all kinds of photography (handheld
and tripodbased). You are again fully right in assuming than this c/s
factor is extremely important in all (ab)normal shooting circomstances.
Shooting a 100ISo at f/2,8 at 1/125 in twilight or early morning light
NEEDS a good influx of contrast. Again here Leica deleivers more than most.
Shooting a ISO400 needs even more optical contrast to compenstae for the
low emulsion contrast (CI value) of this type of films. BUT a ISO400 film
does not need very high resolution. That degrades the image quality. The
MTF cut-off frequency is very important here. It is better to have high
contrast at 40 c/mm with a sharp drop than a general tapering off of
contrast. Here again Leica lenses offer a bit more. Thats your 'punch'. I
hope I gave you a good expalanation of it.

>I do not have time to go on with this today. And i am not qualified to do
>so anyway. I revert to Erwin's original post on this matter and keep on
>wondering if the defense of the Leica advantage could be a battle that is
>fought on the wrong battlefield. Personnaly, I LOVE Leica, but not for the
>reasons that come back in most of the posts. Unless you use your Leica like
>a Hasselblad or a view camera, you are not fighting the optical battle. And
>if you are using your Leica the heavy tripod/f5.6/ISO25 way, why are you
>not using the larger formats which bring a REAL imaging advantage ? I do
>not believe available revenue is a dominant constraint in this list, so
>owning and using different systems and formats must be quite common. I find
>it masochistic to annihilate the portability of 35mm...


Good points. But your battlefield is nonexistant. If any 35mm worker (Leica
biased or not) will try to outperform medium format he will fail ultimately.
As you say Leica lenses have punch and contrast and subtle colour rendition
etc which will show up in all hand held shooting situations with a little
bit of care and technique. And will outperform the 35mm competition mostly
if not always.
I am not using my Leica as a 'blad. I am shooting 75% of my time in HCB
conditions, but with Kodachrome 25 and 64. (At 1/250 or even faster I can
substitute for a tripod in all but the most exacting demands). The Leica M
advantage here is the superb rangefinder that allows me to exploit the
inherent optical quality.
BUT when necessary I can shift some gears and get medium format quality
when using a tripod etc.
There is one point I disagree with you. The dichotomy "portability versus
ultimate  image quality" is counter productive. When using my Elmarit-M
90mm at full aperture with a 1/250 and Kodachrome 25 (which can be used in
many outdoor situations) I have portability AND superior image quality. If
I put my M6 on a tripod and use the same lens (now at 5,6 and 1/30 I can
make Hasselblad owners cry) Which is a nice sport (-:).


Erwin