  The optical vortex coronagraph is potentially a remarkably effective device,
at least for an ideal unobstructed telescope. Most ground-based telescopes
however suffer from central obscuration and also have to operate through the
aberrations of the turbulent atmosphere. This note analyzes the performance of
the optical vortex in these circumstances and compares to some other designs,
showing that it performs similarly in this situation. There is a large class of
coronagraphs of this general type, and choosing between them in particular
applications depends on details of performance at small off-axis distances and
uniformity of response in the focal plane. Issues of manufacturability to the
necessary tolerances are also likely to be important.
