Catherine Rogers schrieb:
> I would like to know details/facts concerning the spectral sensitivity of
> Talbot's Calotype emulsion compared to the sensitivity of Vandyke emulsion; and
> of the sensitivity of the Calotype compared to ortho film (or any other film
> anyone may know about).
> For example, does an image (camera) made with ortho film, respond to the light
> spectrum in the same way (or not) as the calotype (also exposed in the camera).
> (Although I guess modern coated lenses play havoc with that too!) Or, would a
> vandyke emulsion (if it were to be exposed in a pinole camera for example)
> respond the same as Talbot's calotype emulsion or the same as his first
> photogenic drawing emulsion (also sometimes known as a salt print) exposed
> similarly?
Sorry, but isn't that an impossible comparison? The calotype negative
was sensitive enough to be exposed in a camera for minutes. How many
hours shold one expose a VDB, as this proces is a printing process and
so much less sensitive? Eder once researched the spectral sensitivity of
the different silver and dichromate systems, but I don't have his books
at hand here in Dessau. Othochromatic sensitisation wasn't invented
before 1873 by H. W. Vogel and such negatives show greens brighter than
calotypes, which are "unsensitized"
> My interest is
> partly to ascertain whether any contemporary emulsion, or combinations, can
> actually replicate Talbot's emulsions (of the 1830s and 1840s) with respect to
> their response to the light spectrum.
Mike Ware did a lot of research on Talbots early processes and their
light sensitivity. The processes are workable, but as you may not have
acces to the same paper Talbot used you may certainly get different
tonal values and colours. Only Richard Morris I think still owns such
paper, but, I assume, not for sale (?).
> I know I could coat paper with photogenic
> drawing emusion and expose it in the camera etc etc,
You could do that (although it isn't an emulsion, the plain paper is
treated with different salted solutions) but you would never get an
image. The photogenic drawing's silver chloride simply isn't sensitive
enough - s. th. Talbot had to learn, too. Just when he used silver
iodide and development (the calotype process) he succeeded.
Klaus Pollmeier