I am a longtime photographer but not such an expert on the technical aspects of optics and digital sensors.
I've been experimenting with my Nikon D200 and a home-made paper pinhole, coloured black on the 'inside'. The RAW images, when viewed at 100%, show a fine grid. Picture below of a very small portion of the image (exported without editing as a jpeg), showing the grid (upper half of the picture - the lower half is a bit of dust or other dirt on the sensor). Taken at (native) ISO200, 30-second exposure. Just out of curiosity, I wonder if any of ye know what it is that creates the grid?
Also, the sensor clearly needs a bit of a clean - and I am also very curious about how it comes that the edges of whatever it is that is on the sensor are diffracted.
Update: I made some more images yesterday evening with the same pinhole setup on the Nikon D200, and headlights of a car showed some of the rainbow effect discussed here: What causes this bokeh / lens flare effect?