Fresnel mirror?

Another mustard ice cream strange bedfello combo.

Has anyone ever reflectivized a Fresnel lens to make a telescope mirror? Can it even be done? Can diffractive zones be masked or otherwise treated? How closely spaced must they be to get a good image at low, high powers?

Jess Tauber

jess tauber said:
Has anyone ever reflectivized a Fresnel lens to make a telescope mirror? Can it even be done? Can diffractive zones be masked or otherwise treated? How closely spaced must they be to get a good image at low, high powers?

It can be done, but the image quality is going to be pretty poor, I suspect. Fresnel lenses are not in general high quality; they are used in environments where you really need the flatness. Mirrors are much harder to make in order to maintain the same wavefront accuracy; the same surface accuracy that would yield a 1/4-wave lens would yield about a 1-wave mirror (both of those being wavefront).

Remember that you cannot grind a Fresnel mirror; they must be molded (unless I'm missing some ingenious manufacturing process).