Talk:Astrograph

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Expanded article[edit]

The original article stated "An astrograph is basically a Newtonian reflector but uses a hyperbolic mirror instead of a parabolic mirror or spherical mirror". I have come across other statements [1] that:

An astrograph is a REFRACTOR with a short focal length and a wide field of view, intended for photographic use. Often the objective of an astrograph has more than two lenses. A Schmidt telescope or a Newtonian aren't astrographs, even if they are equipped for photography, because they aren't refractors. And the Newtonian doesn't even have a wide useful field of view.
  • Is the no. 1 definition of an "astrograph" that it is a REFRACTOR?
  • Or is "astrograph" defined by what it does? ---> Wide field large format photography or imaging of the night sky.

If it is the second definition then a Schmidt camera is an astrograph. If not then my weasel statment "although there are many (usually larger) reflecting designs such as the Ritchey-Chrétien and Catadioptrics such as the Schmidt camera" should probably be removed. (ratting my self out there ;^)). Halfblue 03:06, 18 October 2006 (UTC)

Astrographs are historically refracting telescopes of specific (sometimes exact) focal lengths used for Astrometry. Reflectors were not used for this task because spherical aberration at the film plane defeated the purpose of accurate measurement. Schmidt cameras seem to fall outside of the classification "astrograph" in most reliable references I have seen; maybe because their short F-ratios produce image plates that are non-standard (wide field) so cannot be used in conjunction with other astrographs for measuring. There seems to be a trend in amateur circles to call anything you can mount a camera on an "astrograph", not sure if this is technically correct. Will take a stab at a better definition. MrFloatingIP (talk) 16:35, 10 December 2009 (UTC)

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