First light: 23 November, 2004.
Designed and built by: INAF — Osservatorio Astrofisico di Arcetri, Italy.
Description: Phasing the segmented primary mirror of an ELT is a key work requiring phasing (differential piston correction) and alignment (tip-tilt correction). The pyramid co-phasing wavefront sensor is a prototype that is able to do phasing and alignment of the 72 mirror segments of NAOMI at the same time.
S. Esposito, E. Pinna, A. Tozzi, A. Puglisi and P. Stefanini, 2005, "Pyramid Wavefront Sensor at the William Herschel Telescope: Towards Extremely Large Telescopes", ING Newsl., 10, 17