be mitigated or controlled by wavefront control, as it is incoherent (opposite sides of the stellar disk produce diffracted light components of opposite signs). [@2007ApJ...658.1386S] chose to avoid entirely the problem by using an unobstructed 1.5-m diameter off-axis part of the 5-m Palomar telescope to perform high contrast imaging with the optical vortex coronagraph. While this allows the use of high performance coronagraphs designed for unobstructed apertures, the performance loss due to the use of an aperture considerably smaller than the full telescope is significant.

The solutions previously proposed to mitigate the effects of central obstruction, spiders and gaps are generally suitable for ground-based coronagraphy at a few $\lambda$/D IWA, with a raw contrast around $10^{-5}$, as reported by [@2008AA...492..289M] who performed a study of coronagraphic performance on ELTs including realistic assumptions on the level of residual wavefront error after an extreme-AO system. For most of the coronagraphs, central obstruction and spiders were found to have a major impact on performance, limiting the achievable contrast to $10^{-4}$ in the 1 to 4 $\lambda$/D separation range. The notable exceptions to this rule were the Achromatic Interfero Coronagraph , which is insensitive to centro-symmetric pupil features (such as a central obstruction or 