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It is not necessarily the case that the Gregorian is shorter than the Newtonian. Given the same primary mirror, the Gregorian will be longer, as the seconday mirror is outside the focus of the primary mirror.

http://bobmay.astronomy.net/johnpierce/part9.htm

The first reflection from the bottom-most green light-path doesn't make any sense. I mean it should be under the purple one, not on top of it.

Falkartis ( talk) 14:35, 15 September 2016 (UTC) reply

In the sentence beginning, "In the Gregorian design, the primary mirror," I changed "an actual image" to "a real image." 75.28.97.105 ( talk) 19:18, 10 July 2017 (UTC) reply