Quote Originally Posted by Stephen Benskin View Post
BTW, I don't see the ZS EI as being designed for the discriminating taste of the photographic elite. It's just the safety factor from before 1960. All anyone has to do is take the ISO film speed and cut it in half.
That's a short-circuit (which I occasionally do) by taking the usual outcome without stepping through how to get there...

Steps for testing for Zone System film speed are well (and inconsistently) documented... There isn't any intention to include a safety factor. Its a specification of quality that shadow detail is required.

And it may not correlate to the first excellent print criterion, the negative that fits Grade 2 under Zone System, may well be exposed a stop above the "first excellent" print.