"Darkroom User"
wrote in message
news

IanG;886420 Wrote:

PYROCAT HD GIVES FINER GRAIN, BETTER SHARPNESS AND MORE
TONALITY THAN
D76, ALTHOUGH ORIGINALLY DESIGNED FOR LF NEGATIVES IT'S
ALSO USED FOR
35MM &120 NEGATIVES.

In addition the negatives are extremely easy to print
from, with
excellent highlights and shadow detail.

It's also a better developer for making negatives for Alt
processes.

Ian
If it gives finer grain as well as better sharpness than
D76, then it
must be good.
Will I actually see these differences with FP4 Plus and
T-Max 400?
What dilution and times for the small Paterson-tanks?




--
Darkroom User
Well, finer grain is open to the question of how that
was determined. Lots of developers yield finer grain than
D-76, some modern ones, notably Xtol, also deliver somewhat
higher speed but most fine grain developers loose some
speed.
Pyrochatichin, which is related to pyrogallic acid but
is a different chemical can be used in developers which have
strong edge/border effects. This gives the illusion of
sharpness. There is another effect of certain developers
containing pyro and its relatives, that is that it tans the
gelatin image wise. The variation of index of refraction
after development can lead to a similar kind of edge effect
which is visualized as "acutance" or the impression of
sharpness. Note that "acutance" is a Kodak term for this
illusion. High acutance films do not, in general, increase
resolution, in fact they may reduce it. However, where one
is working with small negatives acutance effects will
partially compensate for the lack of sharpness in the
lenses. Note also that border/edge effects, and hense
acutance, is of a fixed scale so that its effect is
dependant on the magnification of the image on viewing. It
can have a quite significant effect on 35mm negatives but
will be virtually invisible on a 4x5.
Graininess also gives the illusion of sharpness. A
somewhat blurry image when overlayed with a sharp grain
pattern will appear to be sharp, at least at first.



--
Richard Knoppow
Los Angeles, CA, USA