From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 07/20/02-03:40:27 PM Z
At 03:15 PM 07/20/2002 -0300, you wrote:
>DEAR LIST,
> I have been following this thread while recovering from a flu I picked
>up at a fencing coach's training camp in Montreal.
> One thing that no one seems to mention when discussing film/developer
>combinations is acutance. Classically, the trade off was grain vs.
>acutance which is perceived sharpness. Finer grain developers produced more
>possible detail and subtle tonal separation but less acutance ("softer"
>looking image). This was often due to the absence of edge effects in fine
>grain developers. Often grainier developers had more edge effects and
>provided images with more acutance which appeared sharper due to exaggerated
>edges.
> I find T-max developer to provide images VERY low in acutance...no edge
>effects. When I want to flatter a portrait subject and minimize the fine
>facial detail (euphemism for lines and blemishes) I use T-max 100 film and
>T-max developer.
> For most of my personal black and white work I use T-max 400 with PMK.
>What I love about PMK is that it produces very fine grain, decent film
>speed, AND GREAT acutance due to the edge effects of the pyro and the highly
>diluted developer.
>I am about to try Xtol because it is less toxic, nonstaining (faster
>printing for most alt processes), fine grain AND supposed to deliver high
>acutance.
> Just some food for thought.
> CHEERS!
> BOB
>
One effect of staining Pyro developers which is often neglected is
differential tanning of the emulsion. Pyro produces a reaction product
beside the pigment which tans the gelatin. Since it is produced in
proportion to the silver it tans the gelatin in proportion to the image
density. This tanning results in increased acutance and some compression of
highlights because it slows down the diffusion of developer into the harder
areas.
Where there is a large amount of differential hardening it can be seen as
a relief image when the emulsion surface is examined by reflected light.
The pigment stain image tends to smooth out grain.
I've never seen any tests on its effect on resolution but it is probably
lowered, not a big deal. Staining Pyro developers are avoided in photo-
grametric work and astronomical photography because the localized tanning
effect can distort the local image.
---- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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