Impact of the spider thickness on the CoG measurement. Top: sensitivity to a phase discontinuity (solid lines) and to a phase slope (dashed lines) with respect to the spider thickness. The simulation is carried out with a = 0.05 (weak phase regime). The spider obstructs the subaperture (SA) at the center of the subaperture. The spider thickness varies from 0% (infinitely thin) to 100% of the SA width (full obstruction). Two different fields of view (FoV) are tested. Bottom: 1D illustration of the free parameter, the spider thickness, in both the phase discontinuity (left) and the phase slope (right) cases.