Comment by lucb1e

The concentric rings of increasing blurriness remind me of a Fresnel lens. I'm no optician and always found the physics of light rays confusing as heck so the only words I understand from the wikipedia aricle are "A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet." Maybe someone else can tell whether that's what's being used here? https://en.wikipedia.org/wiki/Fresnel_lens