  We model weak gravitational lensing of light by large-scale structure using
ray tracing through N-body simulations. The method is described with particular
attention paid to numerical convergence. We investigate some of the key
approximations in the multi-plane ray tracing algorithm. Our simulated shear
and convergence maps are used to explore how well standard assumptions about
weak lensing hold, especially near large peaks in the lensing signal.
