of being scrapped due to a ballooning budget, whilst the aperture had been reduced to . A panel known as the Tiger Team was convened to reduce the cost; a re-design cut the price-tag by 45%. Savings were primarily made by reducing the focal length of the telescope – which allowed the use of a smaller dome – and relocating non-essential functions outside the dome to a simpler (and thus cheaper) rectangular annexe. In the same year, the Isaac Newton Telescope was moved to Roque de los Muchachos Observatory, becoming the first of the Isaac Newton Group of Telescopes. In 1981 the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organization for Scientific Research, NWO) bought a 20% stake in the project, allowing the WHT to be given the go-ahead. That year was the 200th anniversary of the discovery of Uranus by William Herschel, and it was decided to name the telescope in his honour. Construction of the telescope was by Grubb Parsons, the last telescope that company produced in its 150-year history. Work began at their factory in Newcastle upon Tyne in 1983, and the telescope was shipped to La Palma in 1985 (the two other telescopes of the Isaac Newton Group began operating in 1984). The WHT saw first light on 1 June 1987; it was the third largest optical telescope in the world at the time. The total cost of the telescope, including the dome and the full initial suite of instruments, was £15M (in 1984, equivalent to £M in ); within budget once inflation is taken into account. Design Optics The telescope consists of a f/2.5 primary mirror made by Owens-Illinois from Cervit, a zero-expansion glass-ceramic material, and ground by Grubb Parsons. The mirror blank was produced in 1969 as one of a set of four, along with those for the AAT, CFHT and Blanco telescopes, and was purchased for the WHT in 1979, ten years after it was made. The primary is solid and un-thinned, so no active optics system is required, despite its weight of . The mirror support cell holds the main mirror on a set of 60 pneumatic cylinders. Even under the most extreme loading (with the telescope pointing at the horizon, so the mirror is vertical) the shape of the mirror changes by only ; during normal operation the deformation is much smaller. In its most usual configuration, a hyperbolic secondary mirror made