Gravitational Lensing and the search for Dark Matter

Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.

Thanks,
AM

[Mod. note: there are many reviews of this topic that you can find
with a search engine or by searching ADS. For a recent one try
http://arxiv.org/abs/1303.3274 -- mjh]