Fresnel Mirrors can be made with different techniques. This is the simples way to make a Fresnel Mirror. The beam concentrates to a 2 inch diameter which is good for boiling water. The center is filled with the flat cut away circle not shown in this video. This is a great demo project explaining the structure of a Fresnel Lens.
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A Fresnel lens eliminates the bulk of a convex concentrating lens with the use of a series of...