 All optics on the first wheel have an aspheric profile to correct for the Hubble spherical aberration.The FUV channel has two medium and one low resolution spectroscopy modes.The FUV channels are modified Rowland Circle spectrographs in which the single holographically ruled aspheric concave diffraction grating simultaneously focuses and diffracts the incoming light and corrects both for the HST spherical aberration and for aberrations introduced by the extreme off-Rowland layout.