Eighth-Order Image Masks for Terrestrial Planet Finding
  We describe a new series of band-limited image masks for coronagraphy that are insensitive to pointing errors and other low-spatial-frequency optical aberrations. For a modest cost in throughput, these ``eighth-order'' masks would allow the Terrestrial Planet Finder Coronagraph (TPF-C) to operate with a pointing accuracy no better than that of the Hubble Space Telescope. We also provide eighth-order notch filter masks that offer the same robustness to pointing errors combined with more manageable construction tolerances: binary masks and graded masks with moderate optical density requirements. 
Marc J. Kuchner, Justin Crepp and Jian Ge