system
Given the following post, respond as if you're commenting on Reddit:
human
Scientists, what are some mysteries in your respective fields that us lay people might find fascinating?
gpt
For me, it's always been somewhat magical that convex lenses do Fourier Transforms (FTs).  Suppose you had a transparency of a spider on a grid.  If you place the transparency just in front of a lens, the FT of the image appears at the focal plane.  You can even filter out parts of the image if you block parts of the light at the focal plane.  If you place another lens behind the first (so their focal points overlap) you get back an image of the object but with some parts removed!  You can remove the spider from the mesh if you want, all without computers!