I appreciate the input on this, which I will bear in mind.
As to my own practice, I rarely use N-2, mostly N-1, N, N+1, and once and a while greater expansions. For shadows, I may consider what I can expect for a Zone III area in a scene, but I like to expose for Zone II. Less change in speed that way. (Lower on the toe.) Not entirely sure about the wisdom of this; it's just what I do.
As for testing B&W film speed using the 0.1 fb+f methodology, perhaps one can think of this analogously as lowering color film speed somewhat from that recommended by the manufacturer, so as to make sure that there's sufficient detail in the shadows. This is a common practice in color negative photography.
I've always thought that "0.1" for B&W film was selected as
the smallest value that minimizes the exposure needed to, none the less, provide sufficient detail in the shadows. In this regard, shooting B&W film at the mfg. recommended film speed just doesn't cut it. At least, not for me.
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