Extinction correction for the centre field. Top left: original F090W – F200W CMD. The cyan line represents a 4 Myr (log(Age) = 6.65) MIST isochrone with metallicity [Fe/H] = −2.5 dex (solid in the upper main sequence). The red parallelogram shows our selection of UMS stars that we used to derive the extinction by placing them back onto the isochrone. Top right: extinction-corrected CMD. Bottom left: normalised histogram of the derived extinction values A_F090W. The mean is at 1.31 ± 0.20 mag, and the arrow in the top left panel corresponds to this extinction. Bottom right: map of derived extinction values. The smooth appearance is caused by the smoothing parameter ϵ.