@hananc Yeah, on B+W film you could stop down (or up!) to change contrast and also the granularity of the resulting image when shooting with older-style emulsions/films. You could also do it to bracket and compensate for a high-contrast scene where your meter does not have a narrow enough 'spot' function.

@hananc I've never seen this effect with either digital or film. I'm going to guess that what you're seeing is an increase in sharpness in objects behind (and in front of) the plane of focus as the lens is stopped down, which your eye is reading as increased contrast. But that's just a guess. With older lenses, stopping down a little from wide open would increase contrast slightly, but that effect shouldn't persist into the smaller apertures.