1 INTRODUCTION

2 MATHEMATICAL FORMALISM

2.1 Lensing optical depth

2.2 Joint source probability density and fraction of multiply-imaged sources

2.3 Normalized redshift distributions

3 OBSERVATIONAL CONSTRAINTS AND DETERMINATION

4 RESULTS

4.1 Mean lensing optical depth

4.2 Redshift distributions

4.3 Influence of the cosmological model

5 CONSIDERING THE R-BAND CUT-OFF

6 CONCLUSIONS