Response to "Full" film speed and Xtol

I might raise more questions, but think of it this way. The longer you develop, the denser the dark portions of the negative (highlights) get. Think of it as the "adjustable" parameter. The less dense portions (the shadows) aren't affected nearly as much by development time. If you look at a family of curves showing different development times, they pivot (more or less) around the lower portion (the toe) of the curves. Film speed is based on the density at the lower portion of the curve, the shadow area. It's also determined using a specific developer and procedure. So, if a developer "gives full film speed", it really means that it produces the expected shadow density for the film. The highlights are up to you, as any developer will bring them to just about any density, if you adjust the development time. People talk about "full range tonality" or similar statements, and we all think we know what it means, but consider that any film, with any developer, can produce densities that take the printing paper from full black to base white. IMHO, "full range tonality" is a perception that comes from sufficient shadow exposure to give good detail, development to a contast index that matches the subject, certain curve shapes (though I don't know exactly what they are!), and, finally, subject matter lit such that it contains many graduated mid tones. This is all so simple from a technical standpoint- it's just harder than heck to achieve in the real world.

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