D76 and ID11.

I bought some Ilford HP5 Plus and saw that the times for ID11 and D76 used 1+1 are different. I thought they are supposed to be the same formula, so why not the same times?

Because they aren't suggesting developing to the same contrast index, and Ilford's tests are practically based. Also they aren't indentical any longer the buffering's been changed over the years, so minor variations.

Ian

The times for both developers are printed inside the film box. Why would they suggest developing for different contrasts? The stock times are the same, it's different 1+1 times that I don't understand .

At stock dilution they are essentially the same, when dilute the changes in buffering play a greater part in maintaining pH, so there will be variation.

Ilford & Kodak have always used quite different techniques to determine film Contrast Index or gamma, both are laboratory tests and neither truly reflect rael life conditions which is why Ilford now use a more practical testing system "based on a practical evaluation of film speed and is not based on foot speed".

Ian