Quote Originally Posted by NormanV View Post
It is not vignetting due to an obstruction it is because the distance from the pinhole to the film surface is greater at the edges than from the pinhole to the centre and the edges are underexposed. If you curved the film plane or made a centre filter you could reduce the problem. Or it could be done with careful dodging when printing.
Enh, it's true there is noticeable fall-off at wide angles off-axis, but to my eyes the images above show shadows of an irregular "edge" of some sort. The situation you're describing is more subtle and graduated (in my experience).