I think using a water bath for the tank is a good idea. Even
if you fill the tank first and drop the film in (Kodak
recommended procedure) there will still be an effect on the
temperature of the developer. One procedure, I think from color
processing, is to have everything in a water bath.
BTW, I think the statement that +/- 15 seconds makes a
difference probably means +/- 15%. Generally about a 30%
difference in time will cause a one paper grade change in
negative contrast for cubic grain films and about a +/- 20%
change for tabular grain films.
Generally, Kodak states that their time/temp charts are for
a contrast index suitable for diffusion printing. Not sure how
Ilford does this. Ilford has stated somewhere that they do not
use the ISO method for speed measurement, which uses a CI for
diffusion printing, but rather uses a compromise CI between that
for diffusion printing and condenser printing. Means that if
Ilford's instructions are followed the negatives will slightly
lower in contrast than Kodak. Actually, the ISO document has a
chart showing the effect on measured speed for changes in CI so
Ilford in not exactly using a non-standard method, just a
variation of it.
Agitation makes a big difference in results. Both Kodak and
Ilford recommend methods of agitation for different types of
processing, i.e. small tanks, large tanks, tray, continuous
machines. The difference in small tank agitation does actually
make a difference although not a lot.
Controlling temperature and agitation are very important if
you want predictability and uniformity or consistency. The fact
is that B&W photography is very forgiving, you can wander all
over the place and still get decent prints but try doing it twice
in a row.
One advantage that Kodak and Ilford have is knowing how to
make the _materials_ uniform and predictable.
On 11/25/2019 10:38 AM, Dana Myers wrote:
Following-up on my own note:
On 11/12/2019 9:52 PM, Dana Myers wrote:
On 11/12/2019 9:04 AM, Robert Shanebrook (Redacted sender makingkodakfilm for DMARC) wrote:Keep it simple:
Use time-and-temperature to control contrast/density. Yes, T-Max Films are more sensitive to time-and-temperature differences than 3D films. T-Max Film development time differences of +/- 15 seconds are enough to make a difference. For 3Ds 25% is an appropriate difference.
I was just amazed to be reminded just how sensitive T-Max is. Not a bad thing,
just a thing to manage. Way back when, I'd use a Coleman as a water bath
to stabilize temperature, but then I became perhaps a bit lazier and started
adjusting processing time to match temperature, processing between 70F
and 75F depending on the time of year. J-109 gives times for 70F and 75F,
and I've been linearly interpolating over that range.
After writing this, I thought to review my process - specifically, I usually
use stainless daylight tanks/wire reels, mix Xtol 1+1, measure the temp
of the developer and go from there. It occurred to me that the tank/reel
has some influence over the temperature of the developer, so I dumped
spent developer into a plastic cup and measured it. I did this a few times
and found that the developer was warming-up ~2 degF while processing.
This didn't happen back when I used a water bath, of course.
Oh snap. No wonder my T-Max negs still had a bit more contrast than
desired/expected. Linearly interpolating between 70F and 75F, it's
about 18 seconds time per 1 degF - over 30 seconds difference!
Enough processing talk, here's a snapshot from yesterday's dog walk,
400TMY EI320, Xtol 1+1, exposed in a now-vintage Canon EOS Rebel G with
the very pretty EF 50mm 1.4 prime. (it's a quick scan, please ignore the dust/fiber):
https://drive.google.com/file/d/1qVK6ztr3rw-cHMCJwU4UUxv1YiZWd2B7/view?usp=sharing
Cheers,
Dana
