Quote Originally Posted by Monito View Post
How might this occur?

Finely suspended dust particles inside the camera imaged by the infinite depth of field of the pinhole and reflecting light, like dust in beams of sunlight?
Less than perfectly smooth edges of the pinhole?
Yes and nothing can be perfectly smooth. When I make pinhole with the dimple and sand method these patterns are easily seen. With my Zero Image it is less evident, but can still be seen.
The first would lead to varying patterns, the second (if operative) would lead to identical patterns from picture to picture (when conditions bring it out).
yes, flares around highlights will produce similar patterns. I think this is called diffraction.
Your post was ambiguous. Are you saying the patterns of dots are in the same position from picture to picture (when conditions are right to create them)?
Yes similarities in these patterns can be seen. Not necessarily the exact dot pattern, dot for dot in the same place. Sometime a ray of dots that varies in density, or a cloud of dots taking on the same shape.

Sorry that I cannot explain better, this is only from observation, no scientific rigor on my part.