Re: Adjusting development for temperature

<sometime.photographer@[EMAIL PROTECTED]
> wrote in message 
news:2517e945-3930-4201-9ec0-a78511c8b667@[EMAIL PROTECTED]
 Apr 6, 5:38 pm, Andrew Price <ajpr...@[EMAIL PROTECTED]
> wrote:
> On Sun, 6 Apr 2008 12:46:05 -0700 (PDT),
>
> sometime.photograp...@[EMAIL PROTECTED]
 wrote:
>
> [---]
>
> >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?
>
> Check the times for the specific film you're using at:
>
> <http://www.digitaltruth.com/devchart.html>
>
> and then compensate for the actual temperature of your 
> basement, using
> their time/temperature chart:
>
> <http://www.digitaltruth.com/images/time.gif>


Thanks.  This chart is similar to the values in the table, 
but maybe
using a different temperature coefficient?  As you can see, 
the
temperature scale is linear while the time scale is 
logarithmic.
Perhaps the temperature coefficient is the slope of the 
line.

Richard Knoppow wrote:
>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.
> ...

Why didn't I think of looking there?  The film I am using 
has been
discontinued a few years (stored in the freezer meanwhile). 
The chart
for Plus-X only goes down to 65 deg F, though.  Maybe Kodak 
does not
recommend processing at low temps?  Thanks, anyway.

Plus-X tech sheet:
http://www.kodak.com/global/en/professional/sup****t/techPubs/f4018/f4018.jhtml

     65F used to be the "standard" temperature up to the 
early 1940's when it was increased to 68F due to better 
emulsion hardening in manuacture. Much below this one 
encounters problems due to hydroquinone loosing activity, 
but that depends on the pH of the developer. Low temperature 
development is possible and Kodak used to have a brochure on 
how to do it.
     The simple chemical rules for the variation of rates of 
reaction due to temperature and concentration do not always 
apply directly to actual photographic processes because they 
are complex. For instance, development and fixing are 
affected by the diffusion rate into the emulsion which is 
partly dependant on temperature but depends on the history 
of the gelatin so its not simple.
     Kodak appears not to recommend using some developers 
below relatively high temperatures, for instance diluted 
T-Max. In some of the older Kodak charts a preferred 
temperature was indicated by printing the temp in bold type. 
This was around 75F for T-Max and some others. Kodak never 
stated the reason for this but, usually, they had good 
reasons.
     I've found that Kodak's data is usually quite accurate 
although they occasionally blunder.

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