Quote Originally Posted by doughowk
I learned the hard way that Efke 100, as well as other old-fashion films, have severe reciprocity problems. Surprising to me is that Efke 25 doesn't, and may even be a good choice in low-light situations. For example, Efke 100 at 100 seconds requires an exposure of 20 minutes ; whereas Efke 25 only needs a 2/3 f-stop increase. Not sure about the math or science; but it does suggest that some so-called slow films may be more responsive to low light levels.
Hmmmm...What should I be looking for in the way of knowing if I have done things right? Will the negative be too thin or will it be dense as hell but flat?

PL100 at 3'15" because of a sixty second initial reading with 20% less development time looked pretty good. Nice shadow detail and the highs were not blown out but were pretty thick.

How did you arrive at the 100 seconds equals 20 minutes?

I think I am getting more confused.