Lensing cross section for giant arcs vs. Einstein ring size for a sample of clusters with mass M > 5 × 10¹⁴ h^-1 M_⊙ at z > 0.5 extracted from the MareNostrum Universe. The two panels refer to the two different definitions of the Einstein ring radius. On the left, we use the equivalent Einstein radius, while on the right we use the median Einstein radius. The red solid line in the right panel indicates the best linear fit relation between log (σ) and log (θ_E,med).