[rollei_list] Re: JOBO development tips
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 16 Dec 2013 16:06:21 -0800
----- Original Message -----
From: "CarlosMFreaza" <cmfreaza@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, December 16, 2013 8:17 AM
Subject: [rollei_list] Re: JOBO development tips
Thor:
I couldn't share my experience with you because I
do manual
B&W film processing and never used an ATL 1500 nor
prewash;anyway
developing times have to do with the negative contrast, I
think you
need to find the best neg contrast for your purposes, f.e.
print via
condenser (flatter negatives) or diffuser enlargers ( higher
contrast); it looks like a contrast for a diffuser enlarger
is better
to scan negs for digital prints. BTW, variable contrast
papers and
their filters help very much to compensate the negative
features and
the differences Condenser vs Diffuser enlargers are not so
significant.
Carlos
The presoak affects the take up time for the developer
so it has some effect on total development time for a given
contrast. The effect depends on everything, film,
temperature, developer, and must be determined by
experiment. Kodak used to recommend a pre-soak for
processing sheet film by hand to prevent the sheets from
sticking together when first introduced to the developer. I
think JOBO recommends a pre-soak to slow the penetration of
the developer when it is poured into the tank so as to
eliminate streaks due to uneven development.
To add to what Carlos says above, Kodak philosophy was
to standardize development contrast based on the expected
type of printer with an aim gamma to match "normal" grade
paper and then chosing contrast grade to correct as
necessary. This is as opposed to zone system processing
where development is adjusted to obtain a fixed negative
contrast based on the scene contrast, again so that all
print on "normal" grade paper. The problem is that the
reproduced contrast of a scene may be considerably distorted
from the original contrast even though the entire range of
brightness will be reproduced as shades of gray. the Kodak
method gives you essentially 1 to 1 brightness reproduction
for some selected range of scene brightness. The eye likes
to have mid-gray tones reproduced 1:1 even if shadows and
highlights are compressed or clipped, otherwise the scene
may look grayed out or overly contrasty.
Development charts vary with manufacturer: Kodak charts
used to be based on suitable contrast index for diffusion
printing sources, about one paper grade more contrasty than
ideal for a typical semi-diffusing condenser source while
Ilford uses a compromise value. In any case, as Carlos
points out, with variable contrast paper this is of little
significance since the print contrast can be adjusted for
best visual effect from any reasonable negative.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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