Editing Reflecting telescope (section)

====Dall–Kirkham====
{{See also|Modified Dall–Kirkham telescope}}
[[File:Large 1987 0528 0001 .jpg|thumb|Dall-Kirkham reflecting telescope, built by Horace Edward Dall]]
The '''Dall–Kirkham''' Cassegrain telescope's design was created by Horace Dall in 1928 and took on the name in an article published in ''[[Scientific American]]'' in 1930 following discussion between amateur astronomer Allan Kirkham and Albert G. Ingalls, the magazine editor at the time. It uses a concave [[ellipse|elliptical]] primary mirror and a convex [[spherical]] secondary. While this system is easier to grind than a classic Cassegrain or Ritchey–Chrétien system, it does not correct for off-axis coma. Field curvature is actually less than a classical Cassegrain. Because this is less noticeable at longer [[focal ratio]]s, Dall–Kirkhams are seldom faster than f/15.