The UVIS has two spectrographic channels that provide images and spectra covering the ranges from 56 to 118 nm
and 110 to 190 nm. A third optical path with a solar blind CsI photocathode is used for high signal-to-noise-ratio
stellar occultations by rings and atmospheres. A separate hydrogen - deuterium absorption cell (HDAC) measures the
relative abundance of D/H from their Lyman-alpha emission.