  Spectrograph costs have become the limiting factor in multiplexed fiber-based
spectroscopic instruments, because tens of millions of resolution elements
(spectral x spatial) are now required. Catadioptric (Schmidt-like) designs
allow faster cameras and hence reduced detector costs, and recent advances in
aspheric lens production make the overall optics costs competitive with
transmissive designs. Classic Schmidt designs suffer from obstruction losses
caused by the detector being within the beam. A new catadioptric design puts
the detector close to the spectrograph pupil, and hence largely in the shadow
of the telescope top-end obstruction. The throughput is competitive with the
best transmissive designs, and much better in the Blue, where it is usually
most valuable. The design also has milder aspheres and is more compact than
classic Schmidts, and avoids most of their operational difficulties.
