I post the below for Dan Leeson. He is having some computer issue.....
I have been trying to understand the time exposure issues of
Daguerreotype photography. The most important of the various
criticisms levied against the authenticity of the Constanze photo
deal with that specific; i.e., the group could not have stood
still for the many minutes of exposure necessary for that
portrait. The argument is that lengthy exposures would be
particularly unsuitable for the aged, and impossible for the man
leaning over Max Keller in the picture.
To that issue, I contacted Jonathan Danforth whose website
(
http://photographs.danforthsource.com) shows examples of his
work. He specializes in Daguerreotype photography and works in
this medium almost exclusively.
Some of the details that he pointed out deal with the work of an
early Daguerreotype photographer named John Frederick Goddard (b.
1795, d. 1866). He was a chemist and lecturer in science at the
Polytechnic of Central London.
The Daguerreotype process initially was very slow, and attempts
were made to shorten the long exposure times. One method was by
using a fast lens, and Josef Petzval first made one in 1841. I
believe that this is the lens about which Michael Lorenz spoke in
an item posted on this list by David Black. That lens had a
maximum aperture of f/3.6 and was a breakthrough as far as
portraiture was concerned.
But it was not the only effort designed to improve the long
exposure times. A second solution was to make the plate faster by
double sensitizing, and Goddard, who published on the process in
1840, used bromide vapor in addition to iodine to increase the
sensitivity of the daguerreotype. Goddard refumed the iodized
surface of the plate with bromide, and his accelerator, which he
called "quickstuff," could reduce a ten minute exposure to one
minute.
His work was of considerable significance for daguerreotype
photography, as it reduced the required exposure from some
fifteen or even twenty minutes to as little as ten seconds. Since
this work was spoken of in print as early as 1840, it could well
have been in use for the Altötting photograph. Furthermore,
bromide was imported into America from Germany in the 1840's, so
it may have been in use here in the states, though not nearly as
early as in Germany.
Danforth's comment to me, after I sent him a copy of the
Constanze Daguerreotype were as follows:
"1. The man with the bad comb-over in the back row is standing
at a very awkward angle. He would not be able to hold such a
position for very long and certainly not for five minutes.
"2. I see no motion blurs of hands which is a dead giveaway in
most long exposures. People can often keep their heads still but
rarely their hands. Another such giveaway would be eyes but I
can't see the eyes of the people in the scan you sent. The
earliest close-up portraits (1839) featured subjects with
pure-white eyes (from blurring) because they kept moving them
around."
Danforth concluded his comments to me by saying, "I would
estimate that this exposure was likely to be in the 20-40 second
range at the most."
One final point deals with what happens to the Daguerreotype when
the subject moves, or some body part moves during the
photography. What appears in the final photo is not a blur of the
kind present in contemporary photography, but is instead a white
area having nothing present, as Danforth mentioned in the early
1839 close-up Daguerreotype photography of eyes.
The bottom line here is that there is no reason to believe that
this photo was taken with a long exposure, and the technology
existed to allow it to be taken with a very short exposure.
Dan Leeson
Re: Reviving an old photograph of Constanze
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