Klaus
First I'm glad you agree with me on the eye.
<<Terry, I agree that the human eye can perceive a much wider range of tones
while
scanning and adapting to the details of the original scene than can be
recorded
on film or even be printed on paper. We should ask an optician to know how
much
it really is..>>
Second, the number of tones in a particular density range is dependent on
the observer and the conditions of testing such as illumination etc. You can
devise tests to put rough average figures to it, but in any case I do not
believe there is much practical photographic significance in this.
For what it is worth I don't feel that platinum gives an apparently denser
black than some silver materials (although carbon does.) All these materials
can give an adequate black which is what really matters. I think all can be
made to give as many tones as we can see - however many that is.
The Sudek on my wall has a beautiful glow from the highlights, an intense
black in the negative border and looks fine. And that is photogravure and
cost me nothing.
Peter
Peter