In this figure the contrast for the peak of the Airy pattern (top plot) and for the rings from the first until the 10th (bottom plot) is color-coded for different tilt (0 to λ/D over the horizontal axis) and transmission of the outer “annulus” region of the mask (vertical axis). The phase mask diameter is 0.5λ/D, slightly smaller than the one that will provide a perfect theoretical balance. Numerical simulation shows that the optimal nulling efficiency of the phase mask for zero tilt is obtained for a 95% transmission outside of the phase mask. As the tilt is increased, the control of the outer region transmission allows mitigating the degradation of the contrast as can be seen on the pink-blue valley of the color map.