  High redshift sources suffer from magnification or demagnification due to
weak gravitational lensing by large scale structure. One consequence of this is
that the distance-redshift relation, in wide use for cosmological tests,
suffers lensing-induced scatter which can be quantified by the magnification
probability distribution. Predicting this distribution generally requires a
method for ray-tracing through cosmological N-body simulations. However,
standard methods tend to apply the multiple thin-lens approximation. In an
effort to quantify the accuracy of these methods, we develop an innovative code
that performs ray-tracing without the use of this approximation. The efficiency
and accuracy of this computationally challenging approach can be improved by
careful choices of numerical parameters; therefore, the results are analysed
for the behaviour of the ray-tracing code in the vicinity of Schwarzschild and
Navarro-Frenk-White lenses. Preliminary comparisons are drawn with the multiple
lens-plane ray-bundle method in the context of cosmological mass distributions
for a source redshift of $z_{s}=0.5$.
