I can certainly relate to the frustrations of temperature and development times-- temperatures outside the ranges provided in Kodak's table for development in XTOL. But because temperature vs. development appears to be a logarithmic function, I did a little math and statisitics to solve my problems.(posted 9133 days ago)I did so by first finding the logarithm of the development times provided by Kodak (Pub. J-107), thereby making temperature (Celsius) vs. logTime a linear relationship. Then I did a linear regression analysis to determine the equation of the line. And while the coorelation coeffecient (R^2) is not as strong as one might like (r^2 for HP5+, EI800 in XTOL 1:3=0.99787), the whole concept has worked well thus far.
As an example, the equation for HP5+, EI800 in 1:3 XTOL is: logTime= (-0.04485)(Temp C)+ 2.25152. Simply insert the developer temp (Celsius) and solve; remembering to take the antilog of the answer.
Alternatively, one might alson consider visiting the Ilford website (http://www.ilford.com/html/us_english/bw_chart.html#tempconv) and downloading their temperature conversion graph.
Finally, I should add a few disclaimers: (1) I am an amateur, so my present goal is good composition, (2) I also do mostly medium format so grain is less of an issue, (3) I've applied this method to XTOL only, and (4) the most extreme temperatures I've developed at are 61F and 87F.
Should all of this be clear as mud, email me and I'll try to expound