Editing Reflecting telescope (section)

===Gregorian===

{{Main|Gregorian telescope}}

[[File:Gregorian telescope.svg|thumb|500px|Light path in a Gregorian telescope.]]

The '''[[Gregorian telescope]]''', described by [[Scotland|Scottish]] astronomer and mathematician [[James Gregory (mathematician)|James Gregory]] in his 1663 book ''Optica Promota'', employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image, useful for terrestrial observations. Some small [[spotting scope]]s are still built this way. There are several large modern telescopes that use a Gregorian configuration such as the [[Vatican Advanced Technology Telescope]], the [[Magellan telescopes]], the [[Large Binocular Telescope]], and the [[Giant Magellan Telescope]].
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