I had not heard of microlensing prior to reading this article, but apparently both a galaxy and the individual stars both help gravitational lensing to allow astronomers to see details described as :

“[It] enabled astronomers to probe regions on scales as small as a millionth of an arcsecond. This corresponds to the size of a one euro coin seen at a distance of five million kilometers, i.e., about 13 times the distance to the Moon! "