  MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observation) is the
future multi-conjugate adaptive optics system for the ESO ELT that will feed
the instrument MICADO (Multi-AO Imaging Camera for Deep Observations). It will
use the 6 laser guide stars to give a uniform correction on a field-of-view of
approximately 60arcsec of diameter. Tip, tilt and slow focus measurement will
be done on up to three natural guide stars that could be really faint to
maximize sky coverage. The current baseline is to use the reference wavefront
sensor in the visible to acquire the star and center it on the low order
wavefront sensor that has a much smaller field-of-view. In this work we study
this problem focusing on the estimation error of the tilt from the reference
wavefront sensor as a function of star magnitude and atmospheric conditions.
