All the equations are in the spreadsheets, so you may be able to fiddle with it to get a good fit with the Ilford data.
If you like math and are curious how I came up with the equation, I just plotted the time/temp data with the C64 and then manipulated the x and y axis values (ie log, square, square root, etc) until I found a combination that produced the lowest standard deviation for the line (ie, the straightest line). This was not very difficult, as I had to write my own line-plotting program, and distorting the axes was easy. I think if I were to do it again today I would use some software I have been using to fit polynomials to H&D curves. The only problem I have with that is once I have the polynomial equation, I don't have good way to solve it.
Not sure if PE was implying the Manufacturers temp compensation data is good or not. I always used their temp compensation data. I figured it was like ISO testing; that is, I am not likely to have equipment accurate or sensitive enough to dispute the Manufacturer. Is there any value to test and generate a 'personal temp compensation index,' (like doing your 'personal exposure index')? I don't know, but I am always open to ideas. I just figure the thermal properties of mater are similar between my darkroom and the Manufacturer's lab. |