History of the telescope a wider field of view than a classic Cassegrain. During the period 1850–1900, reflectors suffered from problems with speculum metal mirrors, and a considerable number of "Great Refractors" were built from 60 cm to 1 metre aperture, culminating in the Yerkes Observatory refractor in 1897; however, starting from the early 1900s a series of ever-larger reflectors with glass mirrors were built, including the Mount Wilson 60-inch (1.5 metre), the 100-inch (2.5 metre) Hooker Telescope (1917) and the 200-inch (5 metre) Hale telescope (1948); essentially all major research telescopes since 1900 have been reflectors. A number of 4-metre class (160 inch)
Westerlund telescope is detached from the rest of the building in order to reduce vibrations. Above the concrete plate is a metal floor grid to stand on. The telescope is a 0.9 meter classical Cassegrain but with a third rotatable plane mirror sending light to one of the two Nasmyth foci. The effective system is an f/10 but the primary mirror is an f/3. The telescope was built by Astro Optic and there is a sibling telescope at Albonova in Stockholm. The telescope is one of the largest optical telescopes in Sweden. The main camera has since the start been an SBIG