In article <1JednXli6-DByGTanZ2dnUVZ_hWdnZ2d@[EMAIL PROTECTED]
>,
Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
>
><sometime.photographer@[EMAIL PROTECTED]
> wrote in message
>news:bb784f88-9090-4951-a6d9-5f4bb1bbd76c@[EMAIL PROTECTED]
>Given 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.
How about "there is no coefficient"? These are not simple first-order
functions.
--
Thor Lancelot Simon
tls@[EMAIL PROTECTED]
"The inconsistency is startling, though admittedly, if consistency is to
be abandoned or transcended, there is no problem." - Noam Chomsky
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