Upper panel: derived fluxes f_moon from PSF photometry and their uncertainties σ_tot depending on the distance of the Uranian moon from the Uranus position for the 70, 100, and 160 μm filter, respectively. Lower panel: corresponding signal-to-noise ratios (S∕N = ). The dashed vertical line at ≈7.′′8, 11.′′ 1, and 17.′′ 8, respectively (scaling with λ_c of the filter) indicates a radius inside which the uncertainty increases and the S/N degrades noticeably due to PSF residuals.