Set of isochrones outputted by FSPS from the MIST stellar library at different stellar ages in region 1 and best-fit metallicity Z = 0.31 Z_⊙. Each colour represents the same population as it evolves with time, with older populations growing dimer and redder. The solid black line delimits the regions of the diagram in which a magnification larger than a factor of 10⁴ would be necessary to observe the star in at least one of the eight NIRCam filters used in this work at a limiting magnitude of 30. The shaded region is thus the stars that cannot be observed in any filter with these conditions. The arrows mark the turn-off points, where stars leave the main sequence. The corresponding masses indicate the stellar mass at which this transition occurs for a subset of the isochrones shown in the plot.