Illustration of the synthetic data. The model young massive cluster depicted here contains a mass of 2 × 10⁴M_⊙ (∼5 × 10⁴ stars) and has a half-light radius of 1 pc. It contains stars in the mass range [0.01, 100] M_⊙, sampled from a Kroupa IMF. The model cluster was observed with the MICADO instrument simulator at distances from 8 kpc to 800 kpc. Top row: cluster as seen by the central detector of MICADO (covering an on-sky area of 16″ × 16″). Bottom row: 2″ × 2″ window (512 × 512 pixels) at the centre of this detector. This is the area we used for our study. Here the unique structure of the ELT PSF is visible. This figure illustrates the difficulties that observers will face when crowded fields are studied with MICADO and the ELT.