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The title is wrong. These are not Fresnel lenses, they are zone plates, which were also invented by Fresnel.

As a side note, http://en.wikipedia.org/wiki/Zone_plate makes for very interesting reading for those (such as myself) who are unfamiliar with the physics of the wave nature of light.

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Thanks for that link -- I was pretty sure that Fresnel lenses were refractive, and I ended up reading most of the article trying to reconcile the plastic lenses that I've seen with the copper diffraction grating that it seemed to be describing.

Thanks, sorry about the incorrect title.

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