geocoronal background. It follows that
IMAPS is not suitable for viewing stars that have companions of
comparable brightness that are anywhere between about 2 (the
detector's resolution limit) and 1° away. The collimator
transmits about 62% of the incident flux that passes through its
approximately elliptical aperture (semi-axes of 7.4 and 9.6 cm). About
2/3 of the loss comes from mechanical blockage by the grids and
the remainder is attributable to wide-angle diffraction. Precautions in
the design of the collimator were taken to reduce the confusion that
could arise from small angle diffraction spikes. In laboratory tests
where extraordinarily strong emission lines are imaged by IMAPS, no such
spikes are evident.