Top panel: white-light image of the MDLF is shown together with the 600 non-overlapping apertures placed in empty zones not intercepting visible objects in the image. The corresponding median value calculated at each wavelength and consistent with the zero level (black line), 16th−84th percentiles (red and blue lines), and the rms (green line) are reported below the white image. Apertures have a diameter of and the statistics is computed on each aperture by collapsing slices within dv = 300 km s⁻¹. The pattern of the sky emission lines is evident. The increased noise in the range of 5800 <  λ <  6000 Å is due to the emission of the laser used for ground layer AO.