----- Original Message -----
From: "Tom Rittenhouse" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: May 21, 2001 12:24 PM
Subject: Re: Chromogenic B&W Film
> I used to use XP-1 extensively. Souped in the XP-1
> developer (worked better than C41 on XP-1. XP-2 is supposed
> to be optimised for C-41) it was usable from ASA 100 to ASA
> 3200. The grain was about the same but contrast and density
> varied with to film speed. If you changed film speed you had
> to print differently, so prints tended to be inconsistant
> with automated processing if you shot different speeds on
> the same roll.
> --Tom
Tom inadvertantly brings up the beauty of the chromogenics. They
are the films that allow the roll film camera shooter to
actually utilize a meaningful zone system of exposure.
Stay with me on this for a moment. I hope I can make some sense
here.
The traditional B&W shooter has 2 controls at hand. We use
exposure and development to hit a specific contrast range. That
contrast range is the one which prints well on the paper we like
to print on, more or less. So, within this framework of 3
variables, we go to work. So, what happens when we lock in
another variable. The contrast range is already locked, now we
lock the development with the use of the C-41 process (Has
anyone actually tried to push XP-2?? Just curious). So, what we
need is a wide latitude film with a characteristic curve that
will give a different contrast range throughout it's exposure
slope. For example, it may have a somewhat steep slope at the
lower end, flattening out as the exposure increases. This is
what the chromogenics do.
More than once, I have gone off on a rant about exposure ranges
and film latitude. If the scene fits within the film's usable
range, then a usable ( not neccesarrily optimized ) print can be
made from the resulting negative.
Dye image films have an extraordinary usable range. They don't
block up the way silver image films do. XP-1 had a range in
exess of 10 stops. I bet XP-2Super and T-400CN have longer
ranges.
The average scene is less than 7 stops, and is closer to 6
stops.
Go measure some scenes if you don't believe me, but make sure
your meter is colour blind, or else your measurements are
useless.
Tri-X (the favourite film of the PDML, according to Albano's
survey) has a very long toe with a moderate slope. What this
means it that Tri-X has a lot of exposure latitude. It also
means that Tri-X responds well to development controls. I don't
know if this means anything in context, but it just came to
mind.
Anyway, we were talking about exposure controls. The idea is to
fit a particular exposure/development combination into a given
scene. Since the chromogenics seem able to give a variable
exposure slope depending on exactly where the exposure range
sits on it, it is possible to use meaningful zone system
controls with them.
Sometimes we forget that St Ansel invented the Zone system when
emulsions were thick, and had somewhat short exposure ranges.
Now, emulsions are thin, and have very long ranges.
Now, rather than having a long toe, we have a long shoulder.
The Zone system user can work with it, though it is not a
replacement for a darkroom and custom film processing and
printing. I just wish the emulsions were harder and more
permanent.
William Robb
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