Intensity of the Arago spot as a function of the size of the second disk ω, in a linear (top) and log10 scale (bottom). The first disk of diameter Ω = 1.42 m is at 144.3 m from the telescope, the second disk ω is at d − z = 50 cm from the first one. Vertical red dashed lines correspond to limits given in Eq. (6), and the blue dashed line corresponds to the optimal value of Eq. (15). There is an increase in brightness outside these limits.