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I wonder if any creature maybe during the cambrian explosion developed eyes based on zone plates to focus instead of lenses...
slightly long
@nautilee so, it turns out you can actually focus and magnify light using nothing but diffraction
A zone plate is a pattern of transparent and opaque circles (varying degrees of transparency can also improve performance but aren't necessary) that focuses light. It's perfectly flat; you could print one from your printer onto a transparency
They have major disadvantages compared to lenses but because of the way they don't require materials that are actually reflective or refractive they can be used to focus things like x-rays or gamma rays that are very difficult to focus otherwise
@Felthry
what are zone plates