Re: (Fwd) Re: Times and Temperatures

[boblong@xxxxxxxxxxx (Robert Long)]

On Tue, 29 Oct 1996 16:22:27 +0000 (GMT), you wrote:

|* Temperature
|I think that's very critical. I always try to precise as possible: 20 =
deg
|C (that's 68 deg F?)

This is an interesting--if possibly questionable--statement.  In
theory, at least, every film/developer combination can produce uniform
gamma results over a reasonable temperature range.  If you plot
temperature against log (time) for any given gamma you should come up
with a straight line having a negative slope.  Once upon a time it was
standard practice at Kodak and elsewhere to show such curves (or,
rather, families of curves in most cases, with one curve for each
gamma that might be of interest), plotting usually between 75F (~24C)
and 55F (~13C).  When I refer to Photo Lab Index, it was the standard
reference (looseleaf, upgradable) in the U.S. during the 1950s and
reproduced these charts from most major manufacturers.

Photo Lab Inde also printed blank charts on which you could fill in
your own information.  If the developer included only instructions for
70F and 65F and you wanted to work at 20C (68F), you could plot the
two points from the instructions, draw a ruler-straight line between
them, and be confident of any time/temperature point along the line.
I've done it many times, and I've never known a film/developer
combination to fail me in that respect or to vary from the
straight-line behavior in published data.

The slopes of these lines can vary a lot.  But as far as I'm aware,
they're invariably parallel for a given film/developer combination,
though each line will represent a different gamma.  That's not to say
that the negatives will be identical even if a given gamma is adhered
to.  When density is plotted against log exposure, the curves for
different gammas can have quite different shapes, because gamma is the
slope of the straight-line portion of the transfer curve, and the
ankles and knees of the curves, so to speak, can bend away from the
straight-line portions in quite different ways.

So as long as you stay on one of those straight isogamma lines, yes,
the precise temperature may make a material difference at the
shadow/highlight extremes; but no, it should make no difference in
overall contrast, where the emphasis is in the middle values.

|* Agitation
|Also very critical. I noticed a consideable density around the sprocket
|holes (print as white, see my personal Home Page "Andalusia, Spain, May
|1994 ", at the top). This is caused by too heavy agitation. I now only

I'm aware.  As a matter of fact, the 1:1 roll did show some "sprocket
hole streaks" due to the relatively aggressive agitation.

|invert 90 deg first 30 sec and then for 5 sec every 30 sec. I now rearly
|see this phenomena. Ofcourse there is no strong relation with your "flat
|neg" problem

Since your agitation is less energetic than mine, your contrast
*should* be lower, if anything.

|* Exposure
|250 ASA TTF (red 25 "a like") on Minolta X300 doesn't nesecairly mean =
250
|ASA on your camera. But I presume that you bracket anyway, so this is no
|explanation

I do bracket (toward greater exposure for architectural subjects,
toward less exposure for foliage) and I've just switched from 200 to
250 as my base setting.

So it all remains a mystery unless your metering is radically
different from mine.

|Ps I heard that D76 will be taken out of production, is this true?

I inquired of the owner of my local photo shop (no pun, Adobe!), who
usually is pretty hip about such things.  His answer indicated that
there is a "replacement" product of which I'd been unaware.  He said
it has been available for some time and is not selling well, so his
information is that Kodak will just "combine" the two.  Precisely what
he meant by that I don't know, and I didn't like to ask because he
already was waiting on another customer.

Bob Long
(boblong@xxxxxxxxxxx)

------------------------------

Topic No. 10