Just running an idea for a diy fresnel lens past .. [ In the context that parabolic mirrors have been created by rotating a liquid ] The volume left above the parabola is also parabolic, so ...if that volume is used as a mold for casting it should form a reasonable solid lens, at least for concentrating a parallel beam to a point. (?) It then follows that a set of concentric cylinders should form a set of shallow concentric ring-shaped parabolic curves, which would be inefficient as a reflection mirror as reflections near the edge are blocked by the edges - but the shape should then act as a good template for casting a transmission fresnel lens (?) In fact a simple rectangular grid should be ok. Eg an ice-cube mold should work at least for some resins. So - if anyone wants to try it - the idea would be to partially fill an ice-cube tray with resin, rotate it slowly while it sets, then use as a mold to cast the inverse shape.The inverse shape should then be a diy fresnel (I think ) Does that sound realistic ? (The intent being, the lens use as a fairly crude concentrator, not a high-grade optic ). Could get kind of messy though.