Spatial distribution of residual fringes. The figure shows the RMS fluctuations around the continuum intensity at λ = 1565.07 nm ± 0.8 nm in GRIS data. Contours outline umbra, penumbra, and some nearby concentrations of magnetic field. The white arrow points to the center of the solar disk. The horizontal (dashed red) and vertical (dashed blue) lines mark regions where we investigated the residual fringes along the slit (Fig. 6) and for different slit positions (not shown).