The F25NDQ mode with the
FUV-MAMA detector provides broad band imaging with attenuation factors varying between 10
-1 and 10
-4. The full field of view is 25x25 arcsec, but the
F25NDQ filter is unique in that it is divided into four quadrants, each having a different neutral density factor. In clockwise order starting from the upper left these are
F25NDQ1,
F25NDQ2,
F25NDQ3, and
F25NDQ4, where the number appended to each name is the approximate dex ND factor. The R
80 and central pixel flux are unmeasured but assumed to be approximately the same as produced by the
F25SRF2 filter. Approximate dimensions of each quadrant and the default target location in each quadrant are given in
Table 14.30.
If a target would violate BOP restrictions in any quadrant of the F25NDQ aperture, the restrictions regarding pointing close to objects violating safety limits discussed in
Chapter 7 and
STIS ISR 2000-01 will apply. This rule renders the F25NDQ4 quadrant rather useless, and the F25NDQ3 quadrant is redundant with the full field F25ND3 aperture. Also the dividing lines between the quadrants are somewhat displaced from the center of the detector and are not quite parallel to the detector edges (see
Figure 13.83 for a lamp image taken through this filter), so observers for whom the exact locations of the quadrant boundaries are important should consult.
