Star-Cluster Astrometry with Ground-Based Wide Field Imagers

We show the astrometric potential of the Wide Field Imager at the focus of the MPI-ESO 2.2m Telescope. Currently, we are able to measure the position of a well-exposed star with a precision of $\sim$4 mas/frame in each coordinate (under 0.8 arcsec seeing conditions). We present some preliminary results here.