Typical example of the LWE phenomenon, based on on-sky measurements made with the ZELDA wavefront sensor. Left: parametrised PTT wavefront model based on a single ZELDA phase measurement. Right: the aberrated PSF corresponding to this LWE wavefront map, simulated at a wavelength of 1.536 μ m. The PSF displays three notable side-lobes at the location of the first Airy ring (2.5 λ∕D), which correspond to the differential tip-tilt components seen across individual pupil segments in the aberrating phase map.