[pure-silver] Re: Developer and Neg Density
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sun, 25 Jun 2006 15:26:18 -0700
----- Original Message -----
From: "Martin Jangowski" <martin@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, June 25, 2006 1:42 AM
Subject: [pure-silver] Re: Developer and Neg Density
On Sat, 24 Jun 2006, Adrienne Moumin wrote:
However, I am still confused about the comment in your
prior post in response
to Mark's:
"You can loose nearly one stop by developing in either
Kodak Microdol-X or
Ilford Perceptol (they are identical). When used full
strength these
extra-fine-grain developers loose about 3/4 stop when
compared to D-76. The
results will be normal contrast negatives."
in light of your more recent one in repsonse to my post:
"Standard developers will all deliver the same contrast if
the development
time is correct. "
Contrast and density are two different beasts. You can
expose a film with
a given exposure and give it normal development in a
standard developer
like D76/ID-11. The result will be a negative with a normal
contrast and
densities ranging from nearly clear film in the deepest
shadows and
maximum density in the highlights.
You can double the exposure from above and use Perceptol or
Microdol-X.
This will give you negatives like above (normal contrast,
densities
from nearly clear to maximum density) but with finer grain.
It is impossible to underexpose a film and get normal
densities and
contrast with special developers or longer development. All
you'll get is
empty shadows and raised contrast.
Grüße aus Hohenlohe,
Martin Jangowski
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I'm not sure what the current theory is to explain the
variation of film speed with developer type. The old
explanation for loss of speed with extra fine grain
developers is that they rely on the solvent effect of
sulfite to change the formation of metallic silver crystals
from the silver halide. The idea was that if there is enough
solvent it will strip away some of the latent image. A small
amount of solvent action, as in D-76, raises film speed
slightly by making more development centers available to the
developer. This does not explain developers that increase
film speed, like Xtol, T-Max, DDX, etc, usually those
containing Phenidone in some form. Perhaps Ryuji can bring
us up to date on this.
In any case, film speed is measured by specifying a
certain range of density which represents a certain range of
exposure. If one looks at a characteristic curve, which
plots exposure against density, the entire curve slides
toward the left for increased speed or to the right for
decreased speed (assuming the usual convention of the
exposure scale increasing from left to right). The slope of
the curve is the contrast. The contrast is variable in
normal pictorial negatives because the film is seldom, if
ever, developed to its maximum density or contrast. When
development is reduced to reduce the slope of the curve
(again representing contrast) the densities all change too
unless a compensating change in exposure has been given.
Since a condenser light source tend to increase all
densities, it is equivalent to increasing the slope of the
curve. When this is compensated for in development the
highest density in the negative which is usable (highlight
with some detail) will appear to be lower when the negative
is examined by diffuse light. That is, when a negative is
adjusted for a condenser source both the slope of the
characteristic curve AND the maximum density will be
lowered. An increase in exposure is necessary to keep the
lowest densities from becoming too low. Since the effect of
the condenser source is relatively less for the low
densities, and, because the condenser source will also
increse the contrast of most negative blemishes, the minimum
density becomes important.
The important thing is that, assuming a straight line
characteristic, density at all points is a function of
exposure, the slope of the "curve" remains the same. Varying
development will also change density at all points but not
equally, so the slope of the curve, which again represents
contrast, changes.
Sensitometry is the study of how emulsions respond to
light and the relation of the exposure to the final image.
While it is a very complex science its elements are fairly
simple. I think they are important to understand for anyone
intending to do serious work with the photographic process.
The best simplified presentation of sensitometry (which
includes densitometry) I've found is in the old Kodak B&W
film brochures. There is a similar good explanation of the
printing side of this in the old Kodak paper booklets. I
don't think Kodak publishes these any more but they show up
in used book stores occasionally.
I will add that printing paper is nearly always developed
to close to its maximum density, so the contrast is fixed by
the nature of the emulsion. This would probably be true of
film too if it was always developed for its maximum density,
that is, the contrast would also be at the maximum the film
was capable of. This difference is why film can be varied
over a wide range of contrast while printing paper can not
(actually it can if you settle for weak blacks). Note that
the variation in contrast in variable contrast paper comes
from having two or more emulsion components which can be
exposed selectively by the use of color filters rather than
by any variation of development.
Some of this is pretty elementary but nonetheless seems
to get overlooked making it the cause of considerable
confusion.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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