Analytical photon noise variance (in rad², logarithmic scale) as functions of the number, N, of photons per pixel per frame available for the phase measurement at the entrance of various WFSs: the SHWFS (in orange, Rousset et al. 1987), the unmodulated PYWFS (in green, Chambouleyron et al. 2023), the 1.06 λ/D and 2λ/D dot diameter ZWFS (in blue, Chambouleyron et al. 2023, Haffert et al. 2023) and the iMZ in purple for a λ/D (solid line) and 2λ/D (dashed line) diameter pinhole.