We will discuss the fundamental role of photometric surveys of resolved stellar populations in our Galaxy and beyond.  We have recently analysed the old stellar populations, as traced by RR Lyrae stars, observed in low density environments such as the Galactic halo and dwarf galaxies surrounding the Milky Way. This investigation has revealed that small satellites can not have had a major role in building up this old component of the Galaxy, whereas the contribution of more massive dwarf galaxies like the Large Magellanic Cloud (LMC) and/or the still merging Sagittarius dwarf spheroidal galaxy can be significant.  In the near future thanks to Gaia and to the Large Synoptic Survey Telescope these kind of studies will gain much more detail and will be largely extended to the the outskirts of our Local Group (distances 1Mpc).

In the next future, resolved stellar population studies need to be extended even further to explore environments still very poorly known such as the very dense core of Elliptical galaxies in Virgo or Fornax clusters (distances  ~18Mpc). This is very challenging and only possible exploiting the high resolution power of extremely large telescopes (40-m class). Today we need to learn how to deal with the complex modelling of the Point Spread Function across the FoV that result from the use of adaptive optics (AO) modules to assure the diffraction limit from the ground. Stars are ideal test particles to trace the performances that 1) we can reach with today 8-m class telescopes equipped with AO; 2) we expect from the new generation of giant telescopes. We will describe a systematic study of galactic globular clusters in order to understand our current technical capabilities.