6.5 Attenuation Considerations
As mentioned at the beginning of this chapter, there are two instrument parameters which must be specified for imaging: PSA or BOA, and MIRRORA or MIRRORB. With attenuation factors of 100 and 25 respectively, BOA and MIRRORB allow one to observe a large dynamic range of target fluxes. For example, the imaging exposure time calculator indicates that a target with a flat spectrum of 1 FEFU will give a total source count rate of 263 counts sec-1, and a rate of about 26 counts sec-1 in the brightest pixel, using the PSA and MIRRORA. These are both well within acceptable NUV detector safety limits. With the BOA, one could image a target with a flux of 100,000 FEFU at the same count rate. With both the BOA and MIRRORB, the flux becomes 2.5 × 106 FEFU.
