Illustration of the SCC Lyot stop (left) assuming γ  =  20 and diffracted intensity in the Lyot plane with a four-quadrant phase mask coronagraph (right). In both images the area inside the red circle (β  =  1.0) symbolizes the precluded reference positions. The purple, yellow, blue, and green circles correspond to reference positions for which β is equal to 0.4, 0.6, 0.8, and 1.1, respectively.