4MOST metrology system error analysis

The 4-metre Multi-Object Spectroscopic Telescope (4MOST) instrument uses 2436 individually positioned optical fibres to couple the light of targets into its spectrographs. The metrology system determines the position of the back-illuminated fibres on the focal surface of the telescope. It consists of 4 identical cameras that are mounted on the spider vanes of the secondary mirror of the VISTA telescope and look through the entire optical train, including M1, M2 and the WFC/ADC unit. Here, we present an exhaustive study on the expected centroiding errors, including but not limited to lens fabrication errors, seeing, mirror distortions and parallax effects.