Strong lensing cross-section of an axisymmetric lens and a point source. The lens galaxy is a composite model, introduced in Sect. 3.1, with an angular half-light radius equal to the Einstein radius. The left panel shows the effect of varying the slope γ_DM for fixed f_DM; conversely, the right panel shows variations as a function of f_DM with γ_DM fixed. The system is defined as a strong lens if at least two images are detected. Different lines correspond to the difference, Δm, between the source magnitude and the survey detection limit for a point source.