Constant distortion curves R_λ = + R_th (dot-dashed lines), R_λ = −R_th (dot-dot-dashed lines) for R_th = 5, tangential curves (dashed lines), and radial curves (dash-dash-dotted lines) obtained with the exact (thick gray lines) and approximated (black lines) calculations in the lens plane (left panels) and source plane (right panels). Upper panels: NFW model for κ_s = 0.15. Middle panels: PNFW model for and ε = 0.5. Bottom panels: ENFW model for and ε_Σ = 0.4. In the right panels the axes are in units of η₀ = r_sD_OS/D_OL.