  Intensity interferometry is a re-emerging interferometry tool that alleviates
some of the challenges of amplitude interferometry at the cost of reduced
sensitivity. We demonstrate the feasibility of intensity interferometry with
fast single photon counting detectors at small telescopes by utilising a
telescope of diameter of merely $0.5$\,m. The entire measurement setup,
including collimation, optical filtering, and two single photon detectors, is
attached directly to the telescope without the use of optical fibres,
facilitated by the large area of our single photon detectors. For digitisation
and timing, we utilise a Time-To-Amplitude-Converter. Observing $\alpha$ Lyrae
(Vega) for a total exposure time of $32.4$\,h over the course of six nights, an
auto-correlation signal with a contrast of $(9.5 \pm 2.7) \times 10^-3$ and a
coherence time of $(0.34 \pm 0.12)$ ps at a SNR of 2.8 is measured. The result
fits well to preceding laboratory tests as well as expectations calculated from
the optical and electronic characteristics of our measurement setup. This
measurement, to our knowledge, constitutes the first time that a bunching
signal with starlight was measured in the B band with single photon counting
detectors. Simultaneously, this is to date the stellar intensity interferometry
measurement utilising the smallest telescope. Our successful measurement shows
that intensity interferometry can be adopted not only at large scale
facilities, but also at readily available and inexpensive smaller telescopes.
