Segmented imaging reflectors are a great choice for Imaging Atmospheric Cherenkov Telescopes (IACTs). However, the alignment of the individual mirror facets is challenging. We align a segmented reflector by observing and optimizing its Bokeh function. Bokeh alignment can already be done with very little resources and little preparation time. Further, Bokeh alignment can be done anytime, even during the day. We present a first usage of Bokeh alignment on FACT, a 4m IACT on Canary Island La Palma, Spain and further a first Bokeh alignment test on the CTA MST IACT prototype in Brelin Adlershof.
The First G-APD Cherenkov Telescope (FACT) is pioneering the usage of novel Geiger-mode operated Avalanche Photo Diodes (G-APD, nowadays usually called SiPM) for Cherenkov Telescopes. The camera consists of 1440 pixels with dedicated electronics operated at 2 GHz and is installed on a refurbished telescope with a mirror area of ≈ 9:5 m2 at the Canary Island La Palma. The camera was installed in October 2011, and data are taken almost every night since then. The very stable and reliable operation allows to operate FACT from remote without the need of a data taking crew on-site. Over the years, operation became more and more automatic, and the next step will be to switch to fully automatic operation. This results in a very high data taking efficiency. The operation of FACT allows monitoring the long-term behavior of few variable extra-galactic very-high energy sources with unprecedented sampling density as well as testing the behavior of the sensors under harsh conditions. Despite operating also under strong moonlight conditions and therefore collecting far more signals than during dark nights, the G-APDs show no change in their performance or any indication for ageing. Understanding the behavior of the G-APDs under all the varying conditions allows to operate FACT without the need of any external calibration device. The properties of the sensors themselves allow for a high precision self-calibration of the camera.