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Old 06-11-2019, 11:58 AM
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graham.hobart (Graham stevens)
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spectroscopy

I am resurrecting my SA100 spect grid, with probably a colour ZWO 1200 and I am looking for tips re scopes. This will be a dedicated spect scope sitting on top of a solar scope, so does being an achro matter?
I did the calculator on the r Spec website and a sweet spot for spectra was an 80mm f6.5 skywatcher - but it is rather expensive
looking for cheap and cheerful as I have to buy rings also
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Old 06-11-2019, 12:09 PM
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graham.hobart (Graham stevens)
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spect

Does having diffraction spikes as in an RCT affect the spectra?
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Old 06-11-2019, 12:18 PM
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Quote:
Originally Posted by graham.hobart View Post
Does having diffraction spikes as in an RCT affect the spectra?
Probably not enough to be a problem.
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Old 06-11-2019, 01:35 PM
StuTodd
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Hi Graham,

You already have DSLR camera gear?

You can use the SA100 as an "objective grating" by drilling a 32mm hole in the centre of a spare lens cap and inserting the SA100 into that, then put the cap onto a 135mm lens. You will get lovely results, be able to take fantastic multi-spectra images AND no need to buy a scope etc.

Piggybacking a DSLR then means you can track, remove the SA100 lens cap and use the lens for widefield etc etc.

As for your question, no, spikes won't make a difference to your spectra.

Last edited by StuTodd; 06-11-2019 at 01:39 PM. Reason: Spellinz
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Old 06-11-2019, 01:50 PM
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graham.hobart (Graham stevens)
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spectroscopy

Cheers all, excited to try anything as I don't have the time for multi hour long exposures anymore (or ever actually!!)
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Old 06-11-2019, 02:05 PM
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Merlin66 (Ken)
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Graham,
The SA100 works well in any scope. Preferably f5 or greater.
No issue with spider diffraction.
Poor achromats can give rise to "fishtail" shaped spectral images. (See attached)
As you probably know, a mono camera will give better result.
Any other questions, just ask.

http://www.astronomicalspectroscopy.com/How_to.html
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Old 06-11-2019, 02:35 PM
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graham.hobart (Graham stevens)
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spectroscopy

Thanks Ken, I will ask if need be as I know we have an expert in our midst!!
Cheers. Will try for a better scope and mono then.
graz
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Old 06-11-2019, 04:49 PM
StuTodd
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All I was trying to put across is that there is no need to buy a telescope just for using the SA100.

Stu
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Old 06-11-2019, 05:14 PM
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Stu,
No issue, the use of objective gratings is very popular, Uwe has shown some very good and higher resolution results used objective gratings.
The grating is very flexible......spectroscopy 101
It provides the opportunity of gathering Spectral data and practicing Spectral processing.
Check out our webpage for details and other ideas.
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Old 07-11-2019, 06:58 AM
tomfield (Tom)
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Quote:
Originally Posted by Merlin66 View Post
Stu,
The use of objective gratings is very popular. Uwe has shown some very good and higher resolution results using objective gratings.
Indeed, Uwe is a great example of someone who has shown what's possible with a Star Analyser.

Here, link, for example, is a recent posting of his, including a pdf with a nice explanation of the science of the objects he's observing.
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Old 07-11-2019, 07:14 AM
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Linked pdf doc is interesting....
He was using 3 gratings in series, as visible on the image?
Or this is just the way he kept them between uses?


Also, grism arrangement is different, usually there is only one prism (this is my setup)
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Old 07-11-2019, 08:34 AM
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Bojan,
I'm pretty sure he only uses one grating at a time but multiple prisms to correct the different dispersions.
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Old 07-11-2019, 09:19 AM
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https://groups.yahoo.com/neo/groups/...messages/13983

Bojan,
This link gives a better explanation.
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Old 08-11-2019, 05:54 AM
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Quote:
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Bojan,
I'm pretty sure he only uses one grating at a time but multiple prisms to correct the different dispersions.
That was my understanding as well..

The use of multple gratings results in very confusing spectra, it is impossible to separate spurious signals from real ones.
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