The technique and some preliminary results about the study of the luminosity function (LF) of Lyman Alpha Emitters (LAEs) through gravitational lensing (GL) is 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 of these natural gravitational telescopes, and the higher contrast achievable by the TF, will allow the detection of very faint LAEs, not only reaching a step forward in understanding this primordial objects, but also achieving a better determination of the mass distribution on the inner regions of galaxy clusters.