Maximum influence of source properties in terms of the complex source quadrupole ellipticity ϵ_s on the inference of the complex (reduced) shear g when observing the complex image quadrupole ellipticity ϵ close to the critical curve at which |g| = 1. The left plot shows the absolute value of Eqs. (26) and (27) for source quadrupoles aligned parallel and anti-parallel to the (reduced) shear. |ϵ| is larger than |g| when φ − ϑ_s = 0, while the opposite occurs when φ − ϑ_s = π/2. The right plot shows the relative orientation between the measured orientation ϑ of the image quadrupole and the orientation of the (reduced) shear φ for these source ellipticities. Here, as plotted, the maximum deviation occurs for φ − ϑ_s = ±π/4.