Edge sensors for the ELT primary mirror segments

The M1 edge sensors, which are designed and manufactured by the FAMES consortium (comprising Fogale Nanotech in France and Micro-Epsilon in Germany), are the most precise edge sensors ever designed for a telescope. Two on each side of each segment, the sensors can detect when the segments move out of position, even if only by a millionth of a millimetre. A total of 4608 edge sensors will measure the relative positions of all M1 segments, allowing the overall shape of the mirror to be corrected when the segments move out of place. This photo shows an edge sensor test model.