So I've been walking around the past couple of days since this thread started looking at objects illuminated by the sun, trying to put my eye along the axis of the sunlight without casting a shadow on the object. Closing one eye to simulate a camera lens. Today, for example, I was staring at a round pipe for a while (people must have wondered...) and did see that as the pipe curved outward, it did seem to get darker. But nothing as seen in the Weston print.
So are we discussing an optical effect that happens all the time but we just don't notice it that much, or is the effect seen in the Weston print the result of the photographic process -- Mackie lines and such? And thus variable by paper, developer, process, etc? I imagine the answer to both questions is "yes" but perhaps those more in tune with optical matters have a more informed view.