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)
GREGOR Solar Telescope GREGOR Solar Telescope GREGOR is a solar telescope, equipped with a 1.5 m primary mirror. located at the Teide Observatory on Tenerife in the Canary Islands. It replaces the older Gregory Coudé Telescope and was inaugurated on May 21, 2012. First light was on . GREGOR is the third-largest solar telescope in the world, after the Big Bear Observatory and the McMath-Pierce solar telescope. It is aimed at observing the solar photosphere and chromosphere at visible and infrared wavelengths. GREGOR sports a high-order adaptive optics (AO) system with a 256-actuator deformable mirrors and a 156-subaperture Shack-Hartmann wavefront sensor. Efforts are