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)
40-foot telescope an early photo of it that is framed in wood from the telescope, is on display at the Herschel Museum of Astronomy. The telescope was surpassed in 1845 as the largest ever built by Lord Rosse's great reflecting telescope. The image of the 40-foot telescope remains as one of the great icons of astronomy. 40-foot telescope William Herschel's 40-foot telescope, also known as the Great Forty-Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a diameter primary mirror with a focal length (hence its name ""Forty-Foot""). It was the largest