The ratio of flux in the central spaxel to the flux in the central 3 × 3 spaxels for HD 100546, Serpens SMM 1, and NGC 1333 IRAS 4B. The ratio falls linearly above  >100 μm until 190 μm. Second order light contaminates the spectrum at  >190. Because the first and second order light have different point-spread functions, the plotted ratio determines the fraction of first and second order photons versus wavelength. For NGC 1333 IRAS 4B, the continuum flux in the central spaxel falls at  <70 μm, likely because of extinction.