From: Bob Kiss (bobkiss@caribsurf.com)
Date: 12/28/01-05:12:56 PM Z
DEAR RICHARD,
Weeeeeeeeel, we may have to agree to disagree. The ANSI (ASA have
been out of circulation for a few decades) standard has the film developed
specifically to a certain contrast index which has NEVER related to my work
or the work of many other photographers that I have either learned from or
taught. The speed point IS NOT related to minimum density directly but to a
density above base plus fog WHEN developed to the CI which no one ever seems
to use. My professors were Hollis Todd who wrote PHOTOGRAPHIC SENSITOMETRY
(the bible), Mr. Rickmers who, with Todd wrote the book on applying
statistical analysis to sensitometry and T.H JAMES who wrote THEORY OF THE
PHOTOGRAPHIC PROCESS. James was the director of research at Kodak for a few
decades and THEY ALL told me that, though certain tendencies were
manufactured into films (yes, we actually made emulsions, ripened them,
sulfur, gold, and dye sensitized them, then coated and tested them) it is
the FILM/DEVELOPER combination that determines ALL of the characteristics of
the final image. Who am I to argue with both them and the results of the
tests that we conducted as students. I have seen Tri-X, T-max 400, Agfa
Pan, etc. developed to many different speeds, graininesses, contrasts, and
latitudes...it just ain't so that it is done during manufacture. Please
consider reading T.H. James's THEORY OF THE PHOTOGRAPHIC PROCESS.
So we agree to disagree...
CHEERS!
BOB
----- Original Message -----
From: Richard Knoppow <dickburk@ix.netcom.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, December 28, 2001 6:37 PM
Subject: Re: Re. Increasing Film sensitivity
> At 10:05 PM 12/27/2001 -0400, you wrote:
> >DEAR JOHN,
> > I have never seen a conventional film produce an image without
> >development. There is no such thing as a sensitivity "built into a film
> >{only} at its manufacture". ALL aspects of a film are related to a
> >film/developer combination. Yes, of course, some films are faster, finer
> >grain, etc due to manufacturing but all of those properties are
manifested
> >by film/developer/developing condition combinations...not the film
alone.
> >Manufacturing creates tendencies, development determines the extent to
which
> >they are manifested...very much like the ongoing debate about the effects
of
> >genetics and environment on personality traits and abilities.
> > I am not talking about the ANSI standard speed which results from
some
> >very specific exposure and processing conditions (which hardly ever
resemble
> >the practical conditions of use), I am talking about practical usable
speed
> >for each users conditions.
> >And Diafine or the newer version (I forget the name) for T-max films does
> >yield a higher "practical" speed/sensitivity. The first thing I learned
at
> >RIT in 1969 was NOT to believe any manufacturers but to test under our
own
> >working conditions...and test we did until I had sensi-strips and
practical
> >shooting tests on the brain. It was and still is amazing just how far
off
> >most manufacturers claims are...but of course they can claim that it is
due
> >to "my" working conditions. "Not all that glistens is gold..."
> > CHEERS!
> > BOB
>
> I must disagree with a couple of points.
> The speed and grain of a film is pretty much determined by its emulsion.
> Various developers will vary both to some extent but not a lot. Variation
> of speed is perhaps plus or minus one stop due to developer
> characteristics. In general, developers with Phenidone tend to increase
> speed a little, those with lots of bromide or silver solvents tend to
> decrease it.
> Grain is also mostly a feature of the emulsion. Developers with high pH
> and little sulfite tend to cause grain clumping due to migration of the
> developing silver crystals toward each other. Large amounts of sulfite or
> other halide solvent change the way the developer accesses the development
> centers of the exposed halide particles and affect the shape of the
> resulting silver crystals.
> For the most part the shape of the characeristic curve is unaffeced by
> development other than for shouldering off due to local exhaustion
effects.
> The ISO method of speed measurement is based on the German DIN method.
It
> measures speed at a minimum density. The contrast is fixed; a range of log
> exposure and range of resulting log density is specified. This range is
> based on the avarage scene brightness found by measuring many atual
scenes,
> the contrast is about right for contact printing and diffusion enlarging.
> The current ISO standard does not specify a developer, as previous
> standards did. The manufactuer can use any developer but it must be
> specified with the speeds.
> Changing the amount of development changes the contrast and results in a
> different speed point since the minimum density is changed. For the
reduced
> contrast required for condenser enlarging the resulting speed change is a
> loss of about 3/4 stop.
> The purpose of the standard is to give a reproducible method of
measuring
> a fundamental emulsion characteristic so that they can be compared.
Because
> development of B&W materials is far from standardised the _effective_
speed
> may vary from the ISO speed. This is not the case for color materials
where
> processing conditions are highly standardised. The ISO standard for B&W
> negative materials does not apply to color materials, or even to B&W
> materials use for other than still pictorial purposes (another standard is
> used for B&W motion picture negative material for instance).
> Differences between manufacturers specified speeds and those measured by
> the photgrapher may stem from several causes. One is the use of some
> developer other than the one used for the standard measurement, the other
> is simply experimental error.
> Because there is virtually no safety factor in ISO speeds there is very
> little latitude for under exposure. Most films have a tremendous
tollerance
> for overexposure, as much as twelve stops for some. So, shooting film at
> about half the rated speed may result in better tonal rendition than the
> ISO speed.
> A very great deal of research into speed rating methods and tonal
> rendition was done by Lloyd A. Jones of Kodak Labs. He worked and
published
> from the mid 1920's until the late 1950's. The original ASA speed method,
> adopted in 1943, was based on his "Kodak Speed" method. This system took
> into account the shape of the toe region by specifying a point of minimum
> usable gradient rather than a minimum density. The minimum gradient was
> defined as being 1/3rd of the straight line gamma. For long toe films it
> put the density up higher than for short toe film. Unfortunately, the ASA
> decided to include a 2.5 X safety factor in the speeds. This resulted in
> excessive density. Kodak's film booklets used to recommend halving the
> exposure.+
> The system proved difficult to use in practice, so around 1958 the ASA
> changed its standard to the German DIN system, which used a minimum
density
> (the same log 0.1 over base and fog used now). At the same time the safety
> factor was reduced to 1.5X, effectivly doubling the speed of all films on
> the market.
> The current ISO system is essentially identical to the 1958 system
except
> it no longer specifies a developer formula. The original standard and the
> revised ones up to the current revision specified a developer, or for some
> versions, two developers. The last one was essentially Kodak D-23.
>
>
> >----- Original Message -----
> >From: <Grafist@aol.com>
> >To: <alt-photo-process-l@usask.ca>
> >Sent: Wednesday, December 19, 2001 4:35 PM
> >Subject: Re. Increasing Film sensitivity
> >
> >
> >> Re the recent question on the possibility of increasing film
sensitivity
> >> after exposure.........After some reflection I would submit that the
> >> "sensitivity" of a film to light is built into its emulsion at
> >manufacture.
> >> After exposure the sensitivity of the film would have been all used up,
as
> >it
> >> were. The chemical structure of the silver halides has been changed by
the
> >> action of light thus creating a "latent" image.Then, all we could do is
to
> >> develop the latent but invisible image as fully as possible. See
previous
> >> postings. Alternatively, another possibility would be to treat the film
> >> BEFORE exposure to increase its sensitivity. But that was not the
> >question,
> >> was it? What we are really thinking about is changing the
manufacturers
> >> rating of a film, innit?
> >> Gordon wrote.......
> >> >This is the practice of treating film after exposure, but prior to
> >> development to >increase a film sensitivity.
> >> See you. John - Photographist
> >
> >
> ----
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com
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