The outer edge of the field is a circle of radius 16 arcmin (defined by the filter wheel). The guide probe is on an xy stage and can cover all of this area except for a small part outside its -y range and a cut-out at large x and y. The inner edge of the field is elliptical with a semi-major axis of 14 arcmin along x and a semi-minor axis of 10 arcmin along y. The ellipse is produced because the autoguider is fed by a flat mirror with a circular hole inclined at to the optical axis. The additional conditions are:and the area with and is also excluded.