Cumulative FWHM for both reference stars (HD 169414 and HD 187642) and science star (HD 179218) in the PAH-1 (top), PAH-2 (center) and Si-6 (bottom) filters as a function of the number of co-added frames following the procedure described in Sect. 3.2. The dashed line is the average FWHM reported in Table 2 and following a Lorentzian fit, whereas the dotted lines correspond to the 3σ boundaries.