Schematic of the field of the four clusters (A3571, A3558, A3560, and A3562). Large solid circles represent the approximate cluster positions; the two small circles between A3562 and A3558 are the groups of galaxies SC 1329 and A1327 (respectively, from left to right; see Ettori et al. 1997 for more detailed maps). Each dotted annulus (or sector thereof) represents the approximate region from which the background for the corresponding cluster was extracted; care was taken in avoiding regions occupied by SC 1329 and SC 1327 and obvious point sources.