The abundance and mass-function of black holes, the last stage of massive star evolution, is fundamental for understanding stellar death, and may provide clues regarding the explosion mechanism of core-collapse SNe, and the birth of BH-BH binaries. The study of astrometric microlensing events is currently the most promising path for detecting isolated black holes. However, ameasurement of an astrometric microlensing event requires an astrometric precision of 1 mas, and high cadence.