  In preparation for the Dark Energy Spectroscopic Instrument (DESI), a new top
end was installed on the Mayall 4-meter telescope at Kitt Peak National
Observatory. The refurbished telescope and the DESI instrument were
successfully commissioned on sky between 2019 October and 2020 March. Here we
describe the pointing, tracking and imaging performance of the Mayall telescope
equipped with its new DESI prime focus corrector, as measured by six guider
cameras sampling the outer edge of DESI's focal plane. Analyzing ~500,000
guider images acquired during commissioning, we find a median delivered image
FWHM of 1.1 arcseconds (in the r-band at 650 nm), with the distribution
extending to a best-case value of ~0.6 arcseconds. The point spread function is
well characterized by a Moffat profile with a power-law index of $\beta$ ~ 3.5
and little dependence of $\beta$ on FWHM. The shape and size of the PSF
delivered by the new corrector at a field angle of 1.57 degrees are very
similar to those measured with the old Mayall corrector on axis. We also find
that the Mayall achieves excellent pointing accuracy (several arcseconds RMS)
and minimal open-loop tracking drift (< 1 milliarcsecond per second),
improvements on the telecope's pre-DESI performance. In the future, employing
DESI's active focus adjustment capabilities will likely further improve the
Mayall/DESI delivered image quality.
