00:00In astronomy, the Ritchie-Chrétien telescope is a special type of grain-break telescope, designed to eliminate optical aberration.
00:06called COMA.
00:07This type of telescope provides a relatively wide field of view compared to a more conventional design.
00:14In the Ritchie-Chrétien telescope, the primary mirror and the secondary mirror are hyperbolic.
00:19It was invented in the early 1910s by the American astronomer George Willis Ritchie, 1864 to 1945.
00:27and the French astronomer Henri Chrétien, 1879 to 1956.
00:32Ritchie successfully built the first Ritchie-Chrétien telescope, with a diameter of 0.5 m, in 1927.
00:40The second example is a 1m model built by Ritchie for the United States Naval Observatory.
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