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Old 29-09-2016, 12:04 PM
Nath2099
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Double Telescope Setups

I've seen a few photos of people's rigs where they have something like a 12"+ reflector, with an expensive 4"+ refractor attached to it. Do you think they'd be using the refractor as a tracking scope and just have too much money, or do people actually collect two sets of data?

If two sets of data, what's the benefit of each set?
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Old 29-09-2016, 12:21 PM
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gaseous (Patrick)
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From Barry Armstead's article in the "projects and articles" section of the site:

"Typically, you would have one telescope on the equatorial mount, taking a long exposure while the mount is tracking. Piggybacking on top of that, would be a second, less powerful telescope, with a guiding camera in it. This guiding camera sends corrections to the mount, based on a star that you have designated it to lock on to. All mounts have some degree of mechanical error in them, but a guiding camera and guiding program like PHD, takes the pain out of it and keeps it all on track."
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Old 29-09-2016, 12:28 PM
Nath2099
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They seriously spend 4 grand plus on a guide scope? Too much money it is then.
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Old 29-09-2016, 12:45 PM
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gaseous (Patrick)
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I'm a purely visual person myself Nath, so can't really comment on the cost specifics, but from what I've seen as a casual observer you can certainly drop a fair chunk of coin on a decent AP setup.
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Old 29-09-2016, 01:59 PM
tonez
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in that case they are both imaging scopes, just of different aperture and focal length. you image through the scope that suits whatever you are going for.
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Old 29-09-2016, 02:06 PM
Nath2099
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Ah ok. that makes sense. They were mostly in fancy home observatories. I guess this saves time unmounting, mounting and aligning scopes.
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Old 29-09-2016, 03:31 PM
el_draco (Rom)
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Originally Posted by Nath2099 View Post
They seriously spend 4 grand plus on a guide scope? Too much money it is then.
There are various ways of guiding but most guiding can be done with a small, low cost refractor or even a modified finder scope. You don't use a guidescope on SCT's because the optics often move slightly as these scopes track (called mirror flop). A separate guidescope wont pick up that movement so we use an "off axis" guider which takes a tiny amount of the light from the main scope.

As to why else you would chuck a 4k scope on top of another telescope, there are several reasons:

1/ If the mount has a lot of capacity and is very high quality, it provides multiple imaging options.
2/ You can attach other equipment to this scope, like a photometer or spectroscope and do several sets of observations.
3/ You can do visual obs through two, or more, different scopes.
4/ You can use the second scope, if its a wide field scope, to track down fainter targets, or image a wide and narrow filed at the same time.
5/ You can show off. Some people are, for example, TAK addicts (and I'll leave it at that.)
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Old 29-09-2016, 04:45 PM
poider (Peter)
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So if the mount has a mechanical error and the guide scope corrects that error.... wouldn't that cause movement whilst the scope catches up with itself, and therefore blur the image?
Peter
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Old 29-09-2016, 08:28 PM
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Atmos (Colin)
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So if the mount has a mechanical error and the guide scope corrects that error.... wouldn't that cause movement whilst the scope catches up with itself, and therefore blur the image?
Peter
The guiding is occurring at scales of a fraction of a pixel in size so as long as the mechanical error is small (not a big jitter) it can be guided out without any noticeable blurring. On a good mount the guide errors are considerably lower than the seeing conditions so the sky covers up the guiding
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