Compared to the conventional spherical lens, a Fresnel lens by the lens divided into a series of concentric circles theoretically infinite number of lines (i.e., the Fresnel zone) to achieve the same optical effect, while saving the amount of material

for these lines, the overall thickness of the lens is reduced; ordinary Fresnel convex lens is actually a continuous curved surface is truncated to a section of a discontinuous change of the curvature as the surface is finely divided, so look like a circle around the lines. Fresnel lenses may in fact be regarded as a series of prisms are arranged in a ring, wherein the relatively sharp edge, and the center of the convex surface is relatively smooth.