Re: Acros Films

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From: Ryuji Suzuki -- JF7WEX (RSuzuki@MIT.EDU)
Date: 01/29/03-01:47:04 AM Z


From: Scott Wainer <smwbmp@starpower.net>
Subject: Acros Films
Date: Tue, 28 Jan 2003 23:43:11 -0500

> I do not like the look of images from Kodak films so I generally
> shoot Agfa or Ilford.

I think it's a quite strong comment :-) I don't like the box design of
new Kodak films, so I haven't really seriously tested any. But I think
films are good, at least pre-2002 Plus-X and TMX are my favorites. The
sodium sulfite argument generally repeated and copied may or may not
apply, and Plus-X is a good case where I think stock D-76 gives you
very good sharpness with very fine grain. I've tried to make MANY
developers for Plus-X just because I like the film, and I make
side-by-side comparison of 14x magnification agaist the strip
developed in D-76H (I usually cut sulfite to 80g and add a bit of
bromide, and make it buffered to pH of 8.60 pm 0.05, but this
modification is not very important) but even accutance developers give
me simply grain-enlarged image with no increase in imagewise
sharpness. If this gives desired effect for your image, it's fine, but
I wouldn't say the image sharpness was enhanced. (80g/L of sodium
sulfite maximizes solvent effect, especially when bromide is
present. In absence of bromide, the difference is practically
negligible.)

I think TMX is a bit more tricky, and some mild accutance developers
help to take advantage of TMX's very good resolution (but not
necessarily very good perceived sharpness).

> My mainstay is landscape/architecture and I find the catechol gives
> sharper/grainless images when diluted 1:1:400 using
> stand-development between 50-90 minutes.

If you mostly do LF, I think you can practically ignore grain unless
you make huge blowups, but I work mostly with 6cm square (new Mamiya
6, not the folding camera) so I value fine grain.

My experience with stand development is not very positive either. I'm
also skeptical about the notion of "compensation" with modern
films. I'm also skeptical about the benefit of two bath development
with modern films. But I like modern films :-) I don't know why.

The "compensation" is supposed to be due to exhaustion of developer in
highlight areas. But modern films contain agents to facilitate
diffusion of developing agents, and to facilitate adsorption of
developing agents to silver halide surface. Also, if developping
agents are to deplete, the rate of chemical development must be pretty
large compared to above two factors. In extremely dilute developers,
modern films raise contrast too slowly for this to be likely. In
addition, film curve in highlight-shoulder region seems mostly
determined by sensitizing agents and other factors during emulsion
making. Some people told me compensation works well with greatly
reduced agitation, but I don't like the idea of reduced agitation --
too risky. People told me time to time some combinations worked well
for them, but I'm not certain how reproducible they are.

Edge effect is a different issue, because if you make the developer
rather sensitive to bromide, which is released from vigorously
developing crystals, you get some adjacency effect. Again, if the
development is not rapid enough, bromide can diffuse out to bulk
solution before it makes any effect. My metol-ascorbate-carbonate
developer was aiming at this.

This solution consists of 0.4g metol, 1.0g ascorbic acid, 1.0g sodium
bicarbonate, 4.0g sodium carbonate monohydrate, 20g sodium sulfite in
one liter of water. I like this developer very much, but it does not
keep well, even if you make a split solution and keep ascorbic acid
very acidic. I did some library research on ascorbic acid chemistry,
and posted a midterm report to pure-silver but I haven't made a final
report yet. I think the reason ascorbate developers don't keep is iron
impurity in chemical agents, especially sodium sulfite. Photographic
grade sodium sulfite may contain 10ppm max of iron, and another 10ppm
of heavy metals as lead equivalent. This is more than enough to act as
oxidation catalyst for ascorbic acid. I've been working on
modifications to prolong shelf life. (Sulfite's preservative action is
very slow at room temperature) One usual strategy is to chelate iron,
but this turned out to be a bad idea. Chelating iron just means
keeping iron in solution, and it does not mean it inactivates iron.
Then, EDTA chelated iron is more active catalyst than bare ferric
iron. (XTOL uses DTPA as the chelator, but I don't have DTPA and I
don't know if it helps or hurts.) Also, the developer's pH range is
not ideal for most commonly used chelators, including EDTA and
DTPA. (there is a very effective iron chelator used to treat iron
poisoning but it's impractical for photographic developers.)
Unexpectedly, I observed that very alkaline developer lasted just as
long as very mildly alkaline developer. So I got some idea, and tried
to add phosphate to make very insoluble iron compounds and precipitate
iron out of the solution. Also, ascorbate makes reversible complex
with borates (the same mechanism as the one where borate inactivates
pyrogallol or catechol) and this provides protection for ascorbate.
There are a few other potentially useful ascorbate esters but I didn't
try them. I also make print developers (for silver-gelatin) based on
the same idea, which gives me a very long tray life. Anyway, I
shouldn't write too much bad thing about iron in alt-process list :-)
If there's any chemist formulating practical ascorbate developers, I'm
willing to exchange information.

Here's one idea for sharpness junkies. Almost any photographic
chemistry book mentions "thickened developer" which is basically a
fine grain developer thickened with thickening agent such as
methylcellulose. The increase of sharpness is clearly stated. It's not
too surprising if it also gives compensating effect. There are two
problems. One is that this developer is very difficult to use because
of very viscous form. How you develop a rollfilm? (spiral reel is not
a very good idea. Maybe a real deep tank and a hunger? Then nitrogen
burst wouldn't work. Some people suggested to make one with a black
PVC pipe.) Another is that there is no known replenishing method that
does not need to discard a lot of thickening agent. I was pursuing
this idea but my priority moved to something else. I think motion
picture industry would have loved the idea of increased sharpness, but
I don't think it was ever used in practice. (Richard, know any?)

Wrote a bit too much :-)

--
Ryuji Suzuki
"You're crazy man, there's no one here but me and my machines!" (Neil Young)

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