Mass reconstruction from combined strong & weak lensing

We describe a new non-parametric method for reconstructing the projected mass distribution in galaxy clusters from their lensing effects on background galaxies. The method combines the strong and weak lensing regimes in a linear fashion and breaks the "mass-sheet degeneracy". We demonstrate the feasibility of the method by applying it to the inner regions of the cluster Abell 2218. The character of our mass map is similar to previously published models, but with unavoidably significant differences.