From: Bob Kiss (bobkiss@caribsurf.com)
Date: 07/20/02-04:02:11 PM Z
DEAR RICHARD,
Again, the question of resolution (discerning fine detail) and acutance
(perception of sharpness resulting from exaggerated edges) are two different
things...and edge effects, whether produced by pyro or any other developer,
do enhance acutance.
Another reason that tanning developers are not used in some applications
is that the tanning creates phase shifts (on the microimage and
microdensitometric scales) due to the different thicknesses of the emulsion
and this can distort results.
CHEERS!
BOB
----- Original Message -----
From: Richard Knoppow <dickburk@ix.netcom.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, July 20, 2002 6:40 PM
Subject: Re: T-MAX
> 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
This archive was generated by hypermail 2.1.5 : 09/19/02-11:11:01 AM Z CST