  Recent works identified resolution limits for the distance between incoherent
point sources. However, it is often unclear how to choose suitable observables
and estimators to reach these limits in practical situations. Here, we show how
estimators saturating the Cramer-Rao bound for the distance between two thermal
point sources can be constructed using an optimally designed observable in the
presence of practical imperfections, such as misalignment, crosstalk and
detector noise.
