RE: Pyro and its effects on contrast

KOUKLIS, KERIK T (Kerik.Kouklis@Aerojet.com)
Thu, 29 Jan 1998 12:49:46 -0800

Perhaps this attempt at a graph may help explain what Sandy is saying.
Think of the "o's" as silver density and the "x's" as silver plus stain
density. While each of these hypothetical lines is linear, their slopes
are different. The bottom line (no pun intended) is that there is a
greater amount of stain in areas of higher silver density, therefore the
difference between silver density and silver plus stain density becomes
greater as you move up the scale. And, to reiterate, because platinum
sensitizer is only sensitive to UV light and the UV light is very blue,
proportionally more of the UV light is blocked by the yellow-green stain
of the Pyro developer as silver density increases. This is what causes
Pyro negatives to exhibit higher contrast relative to UV light than
conventionally processed negatives.

I hope this helps and hasn't further confused the issue!!

|
| x
| x
| x o
| x o
| x o
| x o
| x o
| o
|----------------------------------

Also, Carl mentioned FP4+. I very much prefer to use this film over my
other choice (since I shoot 7x17 my practical choice of films is
limited) which would be HP5+. FP4 has a much clearer base than HP5, and
this goes for "standard" developers as well. I also have found that I
prefer the scale of FP4 and the look of the prints made from FP4
negatives over HP5. I do occaisionally shoot HP5 when I absolutely need
the film speed. I agree with Carl that the film base plus fog level is
approximately the same for pyro and non-pyro negs. Since there is very
little or no silver in the non-exposed parts of the film, there is also
very little or no pyro stain. Terry's suggestion that the negative is
awash with a brown muck simply indicates that he has never tried it.
Conversely, I've yet to try Terry's beloved acid-amidol, but I do intend
to. My mind is open!

Kerik Kouklis
http://www.jps.net/kerik/

> On Thu, 29 Jan 1998, S. Carl King wrote:
>
> > 2) There is a linear but not proportional relationship between the
> silver
> > and stain densities (of the PMK processes negative) as exposure
> (time of
> > devleopment) increases.
>
> I could use more explanation here. How can something be linear but
> not
> proportional? As far as I know a linear relationship is directly
> proportional (example: y = Mx where M is the proportionality
> constant).
>
> - Wayde