Quote Originally Posted by Gerald C Koch View Post
Resolution suffers when the pinhole is not circular. The same problem exists for lenses. The image for a 4 blade iris is not as good as one with more blades. For example one of my enlarging lenses has 20 blades in the iris. The effect is similar to having two images super imposed, one taken at f/2 and one at say f/8.
Fascinating. Ralph has shown us that there is one "optimum" for resolution and another for contrast. If we had an elliptical pinhole, optimum for resolution on one axis, and for contrast on another it might lead to some interesting and subtle effects. For example, a photo of a forest of vertical tree trunks might look different depending on whether the camera was upright or rotated 90 degrees due to the direction that contrast is enhanced. I'd be surprised if it was easy to see the difference, but it would be interesting to try it.

Along similar lines, a few days ago, I saw an image that had a sort of "glow" in the highlights, it caught my eye and I went to look thinking it was going to be a zone plate image, but was just a pinhole. That made me wonder about just adding one or a couple of the zone plate rings ( maybe smaller, "outer" rings ) to add just a bit of that effect to a pinhole image....