  We describe the design of the Commissioning Instrument for the Dark Energy
Spectroscopic Instrument (DESI). DESI will obtain spectra over a 3 degree field
of view using the 4-meter Mayall Telescope at Kitt Peak, AZ. In order to
achieve the required image quality over this field of view, a new optical
corrector is being installed at the Mayall Telescope. The Commissioning
Instrument is designed to characterize the image quality of the new optical
system. The Commissioning Instrument has five commercial cameras; one at the
center of the focal surface and four near the periphery of the field and at the
cardinal directions. There are also 22 illuminated fiducials, distributed
throughout the focal surface, that will be used to test the system that will
map between the DESI fiber positioners and celestial coordinates. We describe
how the commissioning instrument will perform commissioning tasks for the DESI
project and thereby eliminate risks.
