Simplified description of the ZWFS. (a): simplified one-dimensional framework for convolutional derivations; in black, the dot diameter is equal to p and the phase shift is equal to δ. In green, the PSF is approximated by a normalized top-hat function with a diameter a. (b): transfer function of the ZWFS for two cases; in red the dot size is smaller than the PSF, and in blue the dot is larger than the PSF. The optimal case appears for p = a and not p = a/2, as done for the classical ZWFS.