Degradation of the Fe I 6302.5 Å line analysis to lower spectral resolutions, from 700 000 (black) to 250 000 (red), 180 000 (green), and 100 000 (blue). The three panels show the change of the spectral line profile at the disk center (top panel), the corresponding bisectors (center panel), and the center-to-limb variation of the convective shift (bottom panel). The FTS atlas profile is added in yellow. Air wavelengths are given in Å, translated Doppler velocities in m s⁻¹ . Intensities were normalized to the spectral continuum. The different center-to-limb blueshifts (lower panel) were either obtained for the line core (dashed lines) or the average bisector (solid lines).