Quote Originally Posted by Stephen Benskin View Post
The Zone System doesn't have one.
I assume you mean "no safety factor" and that makes sense.

Part of what I see running through ZS thought, discussion, and testing is that everybody's seems to be trying to balance the absolute minimum amount of exposure (so as to minimize grain, exposure time, etc...) against a loss of expected shadow detail. They want to know where the edge of the cliff is.

Many times though it seems that the generic "1/2 box speed" advice is a lot like a parent telling a child to "step back from the edge of that cliff" even though we know its not really a cliff, the slope is just changing; it's not an absolute point beyond which things are unworkable, it's just starting to require more work.

It seems to me that over the years also, lenses/coatings had improved and flare was less an issue, at least in part that allowed the switch to ISO from ASA on a technical basis.