Collimators

Two independent collimators, limiting the PDS detectors' FOV to $1.3$$^\prime$FWHM, can be rocked back and forth (max rocking angle of $3.5$$^\circ$, with five possible intermediate steps at 30$^\prime$, 60$^\prime$, 90$^\prime$and 150$^\prime$), thus making it possible to monitor source and background simultaneously.