But since the scale is relative, you have to have a reference point. In Henry's test, the only reference point I can see is the metered exposure. Henry doesn't state that the lens cap exposure is his reference point, or that it is the exposure he placed at the intersection of the axes, but it must have either been that exposure or one of the other exposures which yielded zero net D.
Originally Posted by Stephen Benskin
Suppose the exposure 6 stops below metered is the first one below metered that yields zero net D, and he decides to start the curve there. The only thing you can say is that this is 1.8 below metered on the relative log H scale, because the metered exposure is the reference point. You stopped down 6 stops below metered. It may be that 5 2/3 stops below metered also yields zero net D. Unless you maintain the metered exposure as a reference point, I don't see how you can plot your first non-zero net D exposure at 0.3 relative to a zero net D exposure.
I'm probably not explaining this well. And I admit it is picky, but Henry is picky. That's one of the things I like about him.
I get that it's an arbitrary scale, but it just seems like an odd way to label it if the test is one that bases everything on a metered "Zone V" exposure.