Moiré lenses are cool: two patterned diffractive optical elements are rotated relative to each other to vary the power of the “lens”. Just watch the video (below).
Demonstration of focus-tunable diffractive Moiré-lenses
Stefan Bernet, Walter Harm, and Monika Ritsch-Marte
Vol. 21, Issue 6, pp. 6955-6966 (2013) •https://doi.org/10.1364/OE.21.006955