At times I want a very long depth of field, so I shrink the camera’s aperture way down. I’ve noticed, however, that sometimes these photos are kind of fuzzy. After reading Diffraction & Photography, I realized that I may be getting bitten by quantum mechanics.
In short, shrinking the aperture increases the percentage of photons that act as waves, causing interference patterns. At very small apertures, it is possible for the interference pattern to spill over onto adjoining pixels on the camera’s sensor — causing the picture to start becoming fuzzy.