The amplitude of the initial density fluctuation spectrum from lensing   statistics
  A complete catalogue of galaxy cluster models can be used to constrain cosmological parameters like $\sigma_8$, the amplitude of the initial density fluctuation spectrum. We focus here on two strong lensing statistics for clusters of galaxies: the fraction of rich Abell clusters that are critical to lensing, and the abundance of arcs in such clusters, especially the X-ray luminous ones. The specific aim of this paper is to constrain $\sigma_8$ for the standard Cold Dark Matter scenario within an Einstein-de Sitter universe. 
Eelco van Kampen (Royal Observatory Edinburgh, U.K.)