Isocontours of the deflection potential ψ (black) and surface mass density κ (grey) for an elliptical power law profile lens in physical coordinates x,y. For the purpose of illustration, the contour levels are equally spaced along the diagonals. The slope of the power law profile varies from t = 0.25 (left) to t = 1.75 (right) in steps of 0.5. The axis ratio varies from q = 0.8 (top) to q = 0.2 (bottom) in steps of 0.2.