James,
I thought about that, but the effect seems to be fairly indifferent to the distance of the aperture from the eye. If I understand the Fresnel Zone effect it should pass through several different patterns in short order as the observation point is moved relative to the aperture, with...
If a distant object is viewed through a small ciruclar aperture that is placed close to the eye, there is an apparent "shadowing" of the center of the viewed image, while the inner perimeter of the aperture is bright.
The small aperture enhances the depth of field for good focus, but the...