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)
IRAM 30m telescope IRAM 30m telescope The IRAM 30m millimeter radio telescope is a radio telescope for astronomical observations in the millimeter range of wavelengths, operated by the Institute for Radio Astronomy in the Millimeter Range (IRAM)) and located on the Sierra Nevada, in Spain, close to the Pico Veleta peak. It is the second largest millimeter-wave telescope in the world after the Large Millimeter Telescope, but has to date been much more scientifically productive than its larger competitor. Each year more than 200 scientists from all over the world visit this observatory to explore the universe at millimeter wavelengths, with interests going