This routine scans an external lamp to cover the range 286.5 - 363 nm. On a MKIV, slit #1 is used up to 325 nm. On a MKIII, slit #1 is used up to 350 nm. FW#3 is switched from the NiSO4+UG11 position (242) to the open position (50) during the slit change on a MKIV. This is unnecessary on a MKIII. Also, FW#2 is switched (on a MKIV) to a higher neutral density filter position at 325 nm.