After passing through the PSA or BOA the light travels to one of the optics on the first of two optic select wheels, either one of the three FUV diffraction gratings or the first of the NUV collimation mirrors (table 1), depending on whether an FUV, NUV, or target acquisition channel is selected.
After passing through the PSA or BOA, the light goes to one of the optics on the initial selection wheel. Depending on the chosen channel, it may be directed to either one of three FUV diffraction gratings or the first NUV collimation mirror.