Phase as a function of the spatial frequency. The different plots are models of a binary system with different flux ratio and angular separation. No noise has been added, so the curves represent the perfect case. From top to bottom, the contrast of the primary to secondary decrease. Panels (a)–c)): flux ratio of 1%. Panels (d)–f)): flux ratio of 0.1%. Panels (g)-h)-i)): flux ratio of 0.01%. From left to right, the angular separation gets smaller. Panels (a)-d)-g)): 200 mas. Panels (b)-e)-h)): 100 mas. Panels (c)-f)-i)): 50 mas. In the L′ band, the cut-off frequency of an eight meter telescope is 0.01 mas^-1.