"piterengel" wrote in message
...
On 24 Ott, 01:27, (Thor Lancelot Simon)
wrote:
In article
,

piterengel wrote:

Very long previous thread snipped...............

Today it is arrived the adapter ring I've described above.
So I'll try
with 50 mm enlarger lens first, then with contact print
too. In this
last acse, do you have an approximate idea on time of
exposure? I
think to place the column at least 10 in high with
completely close
diafragm of lens (f/22). so how long could be the
exposition? or can I
try to use an external exposimeter to determine this?

Use an enlarger as your light source. You may have to
put something in to cut down the light. Even a sheet of thin
paper in the negative holder will work. Most exposure meters
will not read low enough to be useful for this but you can
get some idea of needed exposure by knowing that most
variable contrast enlarging papers are around ISO-6 when
used without a filter and around ISO-3 with a medium
contrast filter. Find the exposure for a good print and
divide that by the ratio of paper speed to film speed.
Otherwise you will have to find the exposure by making a
test strip, that is making several exposures about one stop
apart (each double or half the last). You really only have
to do this once to calibrate the setup.
Also, I think it may be possible to use a SLR camera
with a through the lens exposure meter to make the
measurement by laying it under the enlarger and exposing for
about 5 times the white light reading made with a clear
negative (no image) in the enlarger. The reason for the
clear negative is to account for the density of the support
which is considerable for most 35mm negative films due to
the anti-light-piping pigment in them.
I suggested the Leitz Eldia contact printer before
because I think they are not too difficult to find and are
very convenient for this. They were originally meant to
print onto non-color-sensitized slow film of the sort meant
for making B&W motion picture prints. One of these films,
Kodak Fine Grain Release Positive, is ideal but is now
available only in 1000 foot spools. This film has about the
same speed as fast enlarging paper is processed in print
chemicals. Agfa and Ilford made similar films but I suspect
they are long off the market.
Slow, fine grain, pictorial film works fine but most
35mm negative films have a pigment in the support which can
not be removed and makes the slides just a little darker
than the clear support on the printing film. Not a real
problem but you should be aware of it.
For projection the positive needs to be rather contrasty
compared to normal negative contrast. Most of the very slow
fine grain films are inherently contrasty and its possible
to get the necessary contrast and high shadow density with
films like T-Max 100 by processing them is somewhat high
contrast developers like Dektol. I think Kodak has some
limited information on this use but don't know specifically
where it is.
All this makes the procedure look more complicated than
it is. Positive slides for projection were the rule for many
years before 35mm reversal films came on the market, hence
the Eldia and similar devices.


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Richard Knoppow
Los Angeles, CA, USA