Our Optical Blocking Filter (OBF) calibration plan
consisted of five stages. At the University of
Wisconsin Synchrotron Radiation Center (SRC) we mapped the transmission of
all flight-like filters and many of their witness samples at five
energies using a beam of 0.76 mm 
0.76 mm. At the National Synchrotron
Light Source at Brookhaven National Laboratory (BNL) we measured filter
witness samples at hundreds of energies, but only two positions per
filter. At Denton Vacuum, Inc., using a UV/visible/IR spectrophotometer,
we measured the optical/UV
leakage through witness samples to refine the optical constants
for polyimide. At Penn State, we measured changes to the
transmission in filter witness samples as a function of temperature.
The SRC data are critical as they are the only measurements of the flight filters as separate entities, before the filter response is convolved with the response from the CCDs and the AXAF mirrors. These data allow us to search for any large light leaks or manufacturing defects, to measure spatial variations, and to make normalizing bulk thickness measurements to carry over to the high-resolution BNL energy data, which in turn provide detailed transmission models including the effects of EXAFS (Extended X-ray Absorption Fine Structure).