  Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with
large apertures and high image intensities to map the faint Cherenkov light
emitted from cosmic ray air showers onto their image sensors. Segmented
reflectors fulfill these needs, and as they are composed from mass production
mirror facets they are inexpensive and lightweight. However, as the overall
image is a superposition of the individual facet images, alignment is a
challenge. Here we present a computer vision based star tracking alignment
method, which also works for limited or changing star light visibility. Our
method normalizes the mirror facet reflection intensities to become independent
of the reference star's intensity or the cloud coverage. Using two CCD cameras,
our method records the mirror facet orientations asynchronously of the
telescope drive system, and thus makes the method easy to integrate into
existing telescopes. It can be combined with remote facet actuation, but does
not require one to work. Furthermore, it can reconstruct all individual mirror
facet point spread functions without moving any mirror. We present alignment
results on the 4 meter First Geiger-mode Avalanche Cherenkov Telescope (FACT).
