From: TERRY KING, 101522,2625
TO: Pollmeier Klaus, INTERNET:100561.2417@compuserve.com
DATE: 03/06/96 08:41
RE: Copy of: physiology vs. sensitometry
Klaus
You wrote
> The rather emotional discussion between Terry and Peter some time ago
I do not think an attempt to establish the difference between what one can see
and perceive physiologically and what it is possible to record on film
sensitometrically could be regarded as emotional. This a question I have raised
before. It is a seekimg after fact but some seem to regard it as an attack upon
established values.
and Ron
> Silver's valuable remarks on which paper to use for a certain image set me
> thinking. And although discussions on aesthetics and meanings seem not to last
> very long on this list, I'd like to bring it up again.
Even on the Photoart list any opinion not in full accordance with current
'theory' tends to produce unthinking spluttterings from those whose knowledge is
bounded by current theory.
> I believe that 'Photography' as we think of it on this list has nothing to do
> with a correct transformation of original tonal values in a sensitometric
sense.
> The conventional s-curve of silver halide emulsions is WRONG and it remains
> wrong no matter how carefully one reads Ansel Adam's books or any other
> publication on silver halide sensitometry. Human physiology works different.
That is just the point I was making.
The
> Weber-Fechner law applies to opticians but not to artists.
What is the Weber-Fechner law ? How does it apply to opticians subjects ? ( ie
people ). Surely what artists do is art . So an artist has the freedom to
apply this law or not.
Heinrich Kuehn showed
> it clearly: Compared to human perception, silver gelatin emulsions give
> unsufficient contrast in the shadows, place the mid-grey too low and again
give
> unsufficient contrast in the highlights.
But is is possible to produce good high light separation in a pt/pd print
directly from the in camera negative and have good tonal separation in the
shadows maybe seven stops down the scale on a negative. One does not have to
have that range but the results can be beutiful and contribute to the qualities
the photographer/artist was seeking at the time of previsualisation. Of course
that previsualisation could have been an image on the negative with a range of a
stop or less. That is the freedom pt/pd gives the artist.
This drawback can be overcome by
> complex negative masking or to some extent by using the developer DI 13
recently
> mentioned on this list or - of course - by digital image processing. Kuehn at
> his time developed a special two-negative system and a *syngraphic* film with
> two coatings of different speed and contrast. How much the perception of a
scene
> can be improved by adapting a negative's characteristic curve to human
> physiology can be seen through Charles Lewis' illustrations of his article in
> the latest edition of RUNDBRIEF FOTOGRAFIE, which will appear next week.
Two questions:
1. What are the limits of human physiology in this context. This is one of the
points I was trying to establish in the previous correspondence.
2. Are you going to give us an extract of the pertint points from Clarles's
article ?
To be continued in part 2.>
Terry King