The techniques and some preliminary results on the study of the luminosity function (LF) of Lyman Alpha Emitters (LAEs) through gravitational lensing (GL) are presented. Clusters of galaxies, with suitably modeled gravitational lenses, are observed using the tunable filters (TF) of the instrument OSIRIS at the GTC. The combination GLs, and the higher contrast achievable by the TF, will allow the detection of very faint LAEs, reaching a step forward in understanding this primordial objects together with achieving a better determination of the mass distribution on the inner regions of galaxy clusters.