Direct detection of Earth-like planets is one of the major objectives
for the next generation of ground based telescopes (Extremely Large
Telescopes, ELT). ELT instruments will be conditionned by such
scientific programs. Here, we consider here a system made with an
adaptive optics device, a coronagraph and a simultaneous calibration
system. We refined this simple model by including static aberrations
upstream the coronagraph and differential aberrations downstream. Using
numerical simulations, we evaluate how these static aberrations limit
the detectability of telluric planets.