The problem is you'll need a german sense of humour-)))) Ilford products
are easy just watch plenty of Monty Python. I use D-23 and make sure I've
got the stooges on the TV.
 
 Nick

With a little bit of specsmanship and technique change I'll bet
we can say that's actually high precision temperature control:

Start the development at 66F, finish at 70F.  Never more than
2F degrees off, not so bad, eh?

Then convert to centigrade:  20C +/- 1 degree.

It's all how you look at it.

 I find this interesting. The drums don't change enough to matter with
colour printing. Do you just add the tempered developer to the drum? You
could try cooling the drum first. Add tempered plain water to the tank.
That'll drop the temperture inside the tank. Or you could stand the whole
tank in water with a weight on top of it. The first one is quicker. But you
might have to adjust for the water bath some how.

    But isn't B&W printing basically done to completion? Unless things are
so warm the developer changes how it works will it matter?

  Nick

Well, this depends to some extent on the developer.  A developer with a
single developing agent should generally have a straight
time/temperature curve (at least to some lower point where activity
drops suddenly -- this exists for most organic developers, with
hydroquinone being the best known for losing almost all activity below
65 F).  If you use something like Rodinal, it really doesn't matter what
temperature you have (as long as the emulsion will stay on the film
base); just compensate from the published time/temperature chart using
the curve for your dilution.

With a complex developer, OTOH, perhaps one that contains metol,
phenidone, *and* hydroquinone, the curve is non-linear and some of the
agents (HQ) lose activity at a non-linear rate below some temperature;
you might well see a visible difference in tonality, toe speed, grain,
etc. even when compensating for temperature to give the same contrast
(grain is the most likely to change, even with single-agent developers,
because longer in the soup makes for larger grain independent of other
factors).  Loss of activity shouldn't be a problem as long as room
ambient is at or above 68 F.

Kodak's recommendation for 75 F processing with T-Max developer is
because shorter time means less grain, and little else, though it also
hinges on a developer with low enough activity to have small tank
process times of five minutes or longer at that temperature -- you
couldn't process most films in HC-110 Dilution B at that temperature,
because the process time would be under 4 minutes for most common films.
 T-Max, however, isn't the ideal developer for much of anything; you're
better with XTOL, diluted 1:1 or 1:3 (observing, always, the requirement
of 100 ml of stock solution per 80 square inches of film, even if that
means a larger tank to hold the 400 ml of working solution for one 35 mm
film), for practically all modern films.

And with most developers, if your process time is too short, you can
dilute more -- doubling the liquid volume by adding water generally
requires between 1.5x and 2x developing time, and care to maintain
minimum active developer requirements -- though diluting tends to reduce
solvent effects and can convert a fine grain developer into a mild
acutance developer; it can also affect film speed (with most slow to
medium speed films, more dilution gives higher toe speed because
development must be extended to produce normal contrast).

I might mention, I have developed (30 years ago) with HC-110 Dilution B
in a dormitory room with the windows blocked off to make it dark (and
incidentally eliminating ventilation), in the heart of summer, at 95 F.
 Process time was under three minutes, and I got perfectly fine
negatives, though I don't think I'd want to repeat the operation at this
late date...

The situation is better for printing -- diluting Dektol and other print
developers has almost no effect on the print, other than to slow the
process time.  Whatever you're using for print developer, double your
dilution, find your new complete development time, and then adjust for
temperature.  Since prints should be developed to completion anyway, it
won't hurt anything if the print is left in a few seconds too long, but
gross overdevelopment can add fog; best to have a process time of around
two minutes at your lowest temperature (68 F) and adjust to shorter
times (still longer than one minute) for higher temperatures.  With
Dektol, instead of the 1:2 that seems common now (we used to use it 1:1
when I printed in high school in 1974), you can dilute up to 1:9
(according to Saint Ansel) to gain working time -- in his case, this was
for making mural-sized prints, but working at 1:3 instead of 1:2 should
get you enough time to keep your development over a minute even at 75 F.
 Of course, higher dilution in the same tray size means you have to
watch more closely and compensate more carefully for developer
exhaustion -- but that just means you get even more working time, since
the partially used developer takes longer to bring up the print.

Bottom line is that it's more important to have the temperature constant
through the process than to have it at a set figure -- you can pretty
easily compensate for a different temperature, but you can't begin to be
consistent with four degrees of temperature shift during development.

Of course, the high tech solution would be to install air conditioning
in your darkroom.  You can get a small window unit for well under $100,
though cutting a hole in the wall and ensuring it's light baffled will
probably run the cost up.  ;)