Here's a mathematical / procedural pattern to generate the Fresnel diffraction
zones through a circular aperture.

"... the boundaries of successive zones are circles whose radii increase as the
square root of the integers ..."


#declare d = function {sqrt (x*x+y*y)}
#declare ZonePlate = function {ceil (mod (pow (d (x, y, z), 2), 2))}

(green graph, y is proportional to d)

Apparently there's a way of graphing the intensity of the interference bands
against . . . the angle between interfering rays (?) that yields the Cornescu
spiral.

I think that using this with a signed distance function (SDF), this would make a
good way to produce the Fresnel interference in shadows along the edges of
objects.

https://en.wikipedia.org/wiki/Arago_spot

I think the circular moire patterns that show up when it's zoomed out (left) are
an interesting effect.

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