Illustration of the vignetting effect produced by the external occulter. The diffraction pattern of the circular external occulter for an incident plane wave (region: x-axis from 600 mm to 800 mm, y-axis by ±30 mm, origin at the occulter centre) is shown in the background. The geometric edge of the occulter is marked “Oc”, (radius 710 mm), while the stenope image of the Sun is marked “S” (radius of 671 mm). The three circles delimitate intensity beams going through the 50 mm Lyot coronagraph entrance aperture. These correspond to point sources at 914 arcsec (A, occulted), 1000 arcsec (B, vignetting) and 1085 arcsec (C, full illumination) from the solar centre.