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)
Craig telescope 1852 to 1857, erected near London, England. It was a great refractor, a large refracting telescope with an achromatic doublet with an aperture of 61 cm (2 feet (24 inches)) and that was completed in 1852 in Wandsworth Common and dismantled around 1857 (although the brick tower probably survived until 1870). It had a focal length of 76–83 feet. Its namesake, the Rev. John Craig, spent a small fortune to produce a uniquely designed telescope with nearly double the aperture of the next largest refracting telescopes, making it the largest refracting telescope in the World for the better part of