Quote Originally Posted by markbarendt View Post
Your example provides an interesting problem for the ISO standard, "how do I get it to describe what my mid-tones will do in a print?" In a simplified sense, it can't, the question the ISO standard and other shadow point methods answer is just "what the reasonable lower limit?" We still have to figure out how the rest of the film behaves.
Not exactly true. The ISO standard has a "triangle" of conditions/parameters to be satisfied in finding the speed point. It specifies a growth in density to 0.8, 4 1/3 stops up from the speed point of 0.1 above B+F. So there is a required gradient up into the midtones. Granted depending on the film and processing the curve over that range may exhibit varying degrees concavity, but by the time you're into the midtones that is pretty much a non-issue.

In a broader sense, the delta-X method relates the speed point (essentially the basis for shadow point methods) to the fractional gradient method - which was based on print studies, not arbitrary shadow placements.

My two cents.