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)
3.6 m Devasthal Optical Telescope 3.6 m Devasthal Optical Telescope The 3.6m Devesthal Optical Telescope is a clear aperture Ritchey-Chretien style telescope built by Aryabhatta Research Institute of Observational Sciences(ARIES) and is located at the Devasthal Observatory site near Nainital, India. ARIES operates another 1.3m telescope at the same location. The telescope was activated remotely on March 31, 2016 by Indian Prime Minister Narendra Modi and Belgian Prime Minister Charles Michel from Brussels. The telescope optics has been built in collaboration with the Belgian firm Advanced Mechanical & Optical System (AMOS). The 3.6m DOT is currently the largest reflecting telescope in Asia. The telescope intends