Quote Originally Posted by Stephen Benskin View Post
The argument that it’s because a Zone is a range doesn't cut it for me. Just because a Zone is a range doesn’t mean a range can’t be defined and the mid point of that range determined. Adams does offer a target negative density range, and based on that people have extrapolated approximate target densities for the individual Zones.
I see the range between zones defined by the following as well as their midpoints, but perhaps this is not what you mean, IDK:

"It must be understood that these values (i.e. the gray scale values in figure 4-3) are merely points on a continuous scale that ranges from full black to pure white. Each single value represents a range of grays slightly darker and slightly lighter, and the individual gray values produced in a sequence like this one (again, figure 4-3) are each the midpoint of their respective zones." -AA, The Negative