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 made with flint glass by Chance Brothers and a plate glass by Thames Plate Glass Company. The mounting was designed by William Gravatt, and featured a 19.5 meter tall brick tower with a 24.5 m long cigar shaped telescope tube (built by Messrs Rennie) slung from the side. The next largest refractors were two 15 inch (38 cm) refractors built by Merz and Mahler of Münich (Joseph Fraunhofer's firm), one at Pulkovo Observatory in Europe and one at Harvard College Observatory in America. The largest telescope at the time was in Ireland, a 6-foot (183 cm) aperture metal mirror by