Radii of characteristic curves of the spherical NFW lens, plotted as a function of the convergence parameter up to κ_s = 2.1 (left panel) and up to κ_s = 8 (right panel). Included are the radii of the tangential (x_T) and radial (x_R) critical curves, of the tangential (y_T) and radial (y_R) caustics, and of the unit-convergence circle (x₀). The radius of the radial limiting curve (x_R∞ ≈ 1.32) is marked along the right edge of the right panel. The five vertical dashed lines mark the values of κ_s for which critical-curve and caustic dimensions are plotted for the ellipsoidal NFW lens in Figs. 11 and 13, respectively.