20 × 20 Einstein radii (ER) microlensing magnification map computed for QSO2237+0305A with a convergence factor κ = 0.394, a shear γ = 0.395, and a null fraction of continuously distributed matter, using the microlens code (Wambsganss 1999). Caustics are narrow high-magnification features that delineate amplification and de-amplification regions. A circle with a radius of one ER is plotted in the upper left corner.