We propose to use the OSIRIS tunable filters to perform for the first time a systematic study of the environment of Radio Loud and Radio Quiet quasars in windows around a large range of redshifts (z ~ 2 to 4). The aim of our study is (1) to search for the presence of forming clusters of galaxies around quasars, through Ly α emitters, which in turn will allow us to test the current cosmological models, and (2) to investigate any possible relation between the environment of radio loud and radio quiet objects with nuclear activity. These observations will increase our understanding of the early Universe, shedding new light in subjects like primordial starbursts, galaxy evolution, cluster evolution, and AGN formation and fueling, among others. The great capability and flexible nature of the tunable filters make them the most efficient tool for this kind of study.