Does anyone know at what point reciprocity fails with Supra Endura paper. The only data sheet I could find suggested an exposure range of 50 nanoseconds to 10 minutes, is that correct? Maybe that is for the new digi paper. I ask because last night I was making some test strips from a Ultra 50 neg which was even denser than this film normally is. I managed to get everything right with an exposure of 55 seconds (@f5.6). Crazy length of time, but it was quite fun last night watching how colours change as the time lengthened. Anyway, I want to cut this exposure time down and would like to know if reciprocity has failed.