Re: Film Speed and Negative Development

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From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 04/08/03-07:58:50 PM Z


----- Original Message -----
From: "Scott Wainer" <smwbmp@starpower.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, April 07, 2003 8:11 PM
Subject: Film Speed and Negative Development

> Hi all,
>
> Having just bought some Arista Pro 125 (aka, Ilford FP4+)
I decided to run
> some film speed tests. I tried Crawley's FX-37 developer,
Kodak Xtol, and
> D-76/ID 11 and ran into what I consider a problem. All of
the developers
> indicated an EI of about 12-25 with standard development
using a B+W
> densitometer. Increasing dilution and development effected
the highlights
> but not the shadows; the EI still remained 12-25. The
reason for testing
> Crawley's FX-37 developer and Kodak Xtol was that they are
listed as
> increasing speed and sharpness with greater dilutions. I
also tried Sandy's
> Pyrocat-HD developer and found that the film did not
record anything below
> zone IV. All chemistry was mixed from raw chemicals just
prior to
> development. I thought it might be possible that my 35mm
camera's meter was
> off so I took readings with a spot meter and got the same
readings.
>
> Has anyone encountered this problem before? Could my
chemicals have gone bad
> in less than six months? Any ideas on how I can get the
film speed closer
> the manufacturer's rating of 125?
>
> Thanks in advance,
>
> Scott
> smwbmp@starpower.net
>
  I've read the reply where you describe your technique of
measuring.
  To start off, the method specifiec by the ISO is not an
in-camera method. It requires making exposures on a
sensitometer meeting certain specifications, which include
the color of the light source. The film is then developed to
a specified contrast although its not stated as a gamma
value but rather as a density range for a given exposure
range. The measurement is made at a density value of 0.1
over the fog level plus the base density, which can be
considerable for 35mm films.
  The speed varies with the developer. The current ISO
standard does not specify a developer as older versions did.
One can now use any developer but it must be stated along
with the speed.
  Variations in speed from developer type have a range of
approximately +/- 3/4 stop. Developers like Microdol-X, tend
to loose speed, Phenidone based developers tend to gain
speed. Developers like D-76 and D-23 will deliver about the
ISO rated speed.
  Contrast is important. The ISO standard is based on an
effective contrast index about right for diffusion enlarging
or contact printing. Developing to a lower contrast, as for
a condenser enlarger for instance, will result in a lower
speed.
  Ilford claims not to use the ISO method. They don't state
what method they use but I suspect its a variation of the
ISO method but using a contrast value half way between
diffusion and condenser values.
  The ISO method does not include a safety factor so
predicted exposures are about the minimum that will result
in adequate shadow detail. Since nearly all films have
tremendous overexposure latitude (10 or 12 stops for most)
increasing exposure from that given by the ISO speed can
result in better negatives in some cases.
  Measuring speed using a camera introduces a lot of
variables and sources of error. For one thing the flare of
the system (lens flare plus flare from the camera itself)
changes the effective curve shape of the film, lowering the
contrast of the toe region. Since the target density is very
low it will be significantly affected.
  Valid speed measurements are not trivial.
  OTOH, because of the latitude of the film "accurate"
exposure is really not necessary or even meaningful. The
minimum exposure must be such as to place the shadows which
are to print with detail far enough up the curve to be in a
region with reasonably high contrast. L.A.Jones of Kodak
came up with 0.3 of the straight line gamma as the minimum
point, and this was used as the basis for the old Kodak
Speed method. At the same time the brightest objects in the
image, which are to print with some detail, must not be of
such high density as to be beyond the range of the printing
method to reproduce. This is a complicated way of saying
that the film must be developed to a contrast suitable for
the subject and printing material. Zone system stuff
although you can achieve it more simply than using the full
Zone System.
  As far is increasing the real speed of film, i.e., the
ability to record lower minimum exposure for a given
contrast, it can't really be done. Phenidone based
developers, like Xtol, T-Max and T-Max-RS, Microphen, will
yeild about 1/2 to 3/4 stop increase over standard
developers, like D-76 or D-23, but that's the limit. Pushing
means increasing overall contrast to get the toe contrast
up. The result may be to make toe exposures more printible,
but at the price of making the negatives very high contrast.
If the entire exposure is in the toe area the approach
works, but where there are also bright objects in the image
they will become very hard to print requiring lots of
burning or masking.
  so called compensating developers, can be helpful in
recording very high contrast objects by compressing the
values of the brightest parts of the image, but in general,
do not raise toe contrast.
  FWIW, Aristo definitely IS Ilford film. I've even bought
rolls that had Ilford sticky lables on the rolls! Other
materials sold by Freestyle under their house brand may not
be Ilford, at least some of the paper is made by Kentmere
and possibly others.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

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