Spectroscopic throughput will vary with the selected grism. I primary mirror. The dual-beam nature of LRIS now allows obtaining spectra with optimized throughput over a very large wavelength range, and it also allows imaging in two bands simultaneously. For spectroscopic observations, there are many combinations. The choice will depend upon what resolution is needed in the blue versus red, etc.
Some examples appear in the accompanying table.
This is due to a slight obscuration of the field by the internal rails that were installed to carry the dichroics into the beam. This field vignetting is present whether or not a dichroic is deployed, but should not affect any spectroscopic observations. Since many new optical components were installed inside the LRIS spectrograph body, there is the possibility of unwanted internal reflections or scattered light being introduced. While every effort was made to add baffles in several places, it is possible that the internal baffling can be improved. We have found that any failures of blue side mechanisms can often be fixed simply by trying the failed move again.