Varifocal zone plates obtained by moire

Moire patterns in the form of equilateral hyperbolic zone plates have been studied. They are created by a mutual rotation of basic grids which turn out to be zone plates described by conic curves and include as a special case hyperbolic and elliptical zone plates. The obtained moire zone plates change their focal length in function of the rotation's angle between the superposed grids that generated them and therefore they can be of interest in three-point method used for determination of small displacements of great engineering structures. Simulations as well as experimental results are presented.