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Old July 28th 11, 01:30 AM posted to rec.photo.darkroom
Richard Knoppow
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Posts: 751
Default Jobo & Pre Rinse?


"Darkroom User"
wrote in message
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I have bought a Jobo CPE2 with the lift and a 1540 drum
with reels.
I want to use TMax 100 and 400 in D76 1:1. The instruction
book
recommends a 5 minute pre rinse before pouring in the
developer. Is it
essential to pre soak films if using a Jobo?
Does anyone here use a Jobo, if so, what is your method?




--
Darkroom User


There are two reasons Jobo reccomends a pre-soak. One
is that it saturates the emulsion and contols the rate of
uptake of the developer. That insures it is taken up evenly
to eliminate blotching. The development is also slowed
somewhat because the "induction time", that is, the time
between immersing the film in the developer and the time the
image begins to appear, is lengthened. Because of the very
rapid agitation in the drum the development time is quite
short compared to other non-machine methods so that
increasing it a little also tends to insure uniformity. The
second reason is to temper the tank. This is more necessary
for color development done at elevated temperature so that
the temperature of the developer is not suddenly changed
when entering the tank.
Kodak recommends a pre-soak for hand processing of
sheet film in a tray to prevent the sheets from sticking.
While some manufacturers seem to discourage pre-soaking
I can find no very good reason not to.
Elsewhere in this thread it is recommended that D-76
not be used. Some seem to have a predjucide against this
developer but it works very well for many films.
Somewhat higher speed and slightly finer grain can be
had with Xtol. There are other good developers but D-76
remains the standard of comparison after some eighty-five
years.
If Jobo has recommended times I would at least start
with them. I think Kodak may give drum development times for
some film and developer combinations. Otherwise you have to
experiment. Times in a machine like the Jobo are likely to
be surprizingly short because of the very effective
agitation.


--
Richard Knoppow
Los Angeles, CA, USA