  Intensity interferometry for astrophysical observations has gained increasing
interest in the last decade. The method of correlating photon fluxes at
different telescopes for high resolution astronomy without access to the phase
of the incoming light is insensitive to atmospheric turbulence and doesn't
require high-precision optical path control. The necessary large collection
areas can be provided by Imaging Atmospheric Cherenkov Telescopes.
Implementation of intensity interferometers to existing telescope systems such
as VERITAS and MAGIC has proven to be successful for high-resolution imaging of
stars. In April 2022 we equipped two telescopes of the H.E.S.S. array in
Namibia with an intensity interferometry setup to measure southern sky stars
and star systems during the bright moon period. We mounted an external optical
system to the lid of the telescope cameras, which splits the incoming light and
feeds it into two photomultipliers in order to measure the zero-baseline
correlation within one telescope in addition to the cross correlation between
the telescopes. The optical elements are motorised, which enables live
correction of tracking inaccuracies of the telescopes. During the campaign we
measured the spatial correlation curves and thereby the angular diameters of
{\lambda} Sco (Shaula) and {\sigma} Sgr (Nunki), while we also performed
systematic studies of our interferometer using the multiple star system of
{\alpha} Cru (Acrux).
