Re: Adjusting development for temperature

<sometime.photographer@[EMAIL PROTECTED]
> wrote in message 
news:bb784f88-9090-4951-a6d9-5f4bb1bbd76c@[EMAIL PROTECTED]
 that the basement is still coolish from the winter, 
what would
be the best development time factor for D76 at 60 deg F (15 
deg C)?

An experiment with a roll of film at 1.66x recommended time 
yielded a
rather razor thin negative, though the film had been sitting 
in the
camera a year or so.  This time factor was taken from an old 
Manual of
Photography by Focal Press, but it was not specific to D76, 
just part
of a table of suggested factors at a given "temperature 
coefficient".
The Manual refers to temperature coefficient for developing 
agents and
listed a table of factors for a coefficient of 2.75. Here is 
a part of
the table:

Temp:         Factor
15 deg C:  1.66
17 deg C:  1.35
20 deg C:  1.00
22 deg C:  0.82

I am just getting back into B&W film again, after a long 
hiatus.  Any
comments on an appropriate development time for the next 
roll?

Some further searching on Google found the following link 
with some
more details:

"A characteristic, named the "temperature coefficient," has 
been used
as the quantitative measure of the change of activity. This 
is defined
as the ratio of
the development times required to produce equal density at 
two
temperatures differing
by 10°C., which is, of course, a difference of 18°F. The 
values
obtained range from 1.3 for metol alone, through 1.9 for 
pyro and
metol-hydroquinone combinations, to 2.5 for glycine."
  from: http://www.questia.com/PM.qst?a=o&d=97634617
  (in referernce to the book: Handbook of Photography by 
Keith Henney,
Beverly Dudley; Whittlesey House, 1939.)

Thanks for any comments.

    The temperature coefficient varies with the developer 
and to some degree with the film so there is no absolute 
rule. For some guidance check Kodak film data sheets. Most 
have graphs showing the variation of development time with 
temperature as well as showing development times for various 
temperatures on the charts. If you are not using a Kodak 
film you can still get pretty good estimates from this data. 
I think Ilford has similar information on their film data 
sheets. The variation for D-76 and Ilford ID-11 should be 
very much the same although the packaged developers are not 
quite identical.


-- 
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]