Ilustrative example of the degeneracy between the PSF size and spectral type of stars. (a) Middle rows: monochromatic PSFs for two positions in the FOV. The PSFs are shown for eight equally spaced wavelength values. Top and bottom: eight-bin spectral energy distribution of two stars, a M5 star (top) and an O5 star (bottom), located at positions 1 and 2 respectively. The wavelength axis is shared between all rows. (b) Observation of the respective stars.