The coronagraphic mask consists of two circular stops. One is positioned near the circle of least confusion in the center of the aberrated HRC field of view and has a radius of 0.9". The second, which is positioned directly over the Fastie spot, is designed for the brightest targets and has a radius of 1.8". The masks are positioned in such a way that the central wavelength in the linear ramp filters for each is the same, so observations with both can be made without repositioning the filter wheel. The Lyot stop has the effect of removing the diffracted light halo that surrounds the target, giving almost an order of magnitude higher contrast improvement at the longest wavelengths. The coronagraphic spots will reduce the diffracted light from stellar sources by a factor of ~3 at 450 nm. At radii > 3" the diffracted light is reduced by a factor of ~10 relative to WFPC2. (From Ford et al SPIE 1998)
