I use the term "tone reproduction" in the Kodak sense, hope that it will forestall any hairy misconstructs of language such as "tonality" or "creaminess" ...

I remember reading in the Kodak Encyclopedia of Practical Photography the article on Tone Reproduction. It was an explanation of the quadrant approach for understanding how tones evolve over the course of photographic reproduction between the original and the final print.

One of its major conclusion was that "perfect" tone reproduction is not satisfactory to the viewers. In other words, two things in a scene that reflect different amounts of light might look better on paper if they are in fact of the same shade of gray. That's what we call "compressing" tone. The opposite is true: two things in a scene may be very close in the amount of light they reflect, but on a print, this difference needs to be exaggerated to be satisfactory.

Eventually, the Kodak folks figured out which ranges of tones, on average, needed compression, and which ones needed expansion.

So far, if you have ever played with the Zone system, adapted your development for a specific scene, if you know which film/paper combination works better for a given subject, or just changed paper grades to fit a negative, you have a sense of what I'm talking about.

But I'm curious about the role of lenses in this process. We know that flare matters, that it can lower overall contrast, but do we know something about the actual tonal reproduction curve of our lenses?

Reading on painting, today, it made me think how much a lens was important in imaging tones on a negative. It is, after all, a brush of some sorts, light or heavy.

In other words, if your lens was the equivalent of a Photoshop curve, what would it look like? Would it compress or expand highlights? Would it have an upswept, straight, S-shaped, or other curve? How can we reasonably measure or witness it without adding too many variables to control?