If you zoom into the picture (in the upper middle parts) there are a lot of transparent circles/torus shapes. I see exact same things (but didn't pay much attention to it) if I look into a bright light source and squint (especially if eyes are moist from tears). These circles also seem to move. What is it?
If they move, they are probably floaters (little cells or bits of debris floating around in your vitreous humor). In the image, they appear to be diffraction artifacts (airy function) from the pinhole aperture
A flat image was taken for bias subtraction and the debris shows up twice because the projector had moved slightly between images, so the image processing ended up subtracting where it didn’t need to and missing the original artifact.
