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Old 10-27-2018, 08:55 PM   #1
Default Spectroscopy through Orion XT8?

So I scored this great deal when some guy moving to Florida and getting rid of extra stuff put an Orion XT8 Dob on Craigslist for $75. It included the whole beginners kit. 28mm Wide Field, 10mm, 2x Barlow, blah blah and a "solar filter" I chucked in the trash as soon as I saw it.

Unfortunately he bought the telescope without a mount, and tried to "build" a dob mount. He did a poor job and I can see why it went unused all these years. It's a worthless mount with no fine movement and jiggles and bounces. Bearings are non-existent. It's worthless. So instead my brother in law and I are building a big solid equatorial pipe mount for it using plans from All About Telescopes.

But, while I wouldn't go around trying to spy DSO's with the mount, it is good enough to view the brighter objects like the moon(Oh the moon!) and planets. Which is enough to allow me to test the optics. Which are really great. Much better than my 5" Celestron for sure. I think it could use a slight collimation but the collimation piece came with the kit. So I'm good on that as soon as I get moved to my new home.

Anyway, after I purchase a few high grade 2" eyepieces. I'd like to start doing spectroscopy. I'm especially interested in capturing the spectra of eclipsing binaries and maybe the spectra of lunar occulations of stars and such.

I'm still unclear on how these thing work through an eyepiece. Not just being able to record and analyze the data on a CCD of some sort, I'd like to be able to put a high magnification eyepice on the telescope with one of these screw on gratings on.

Would I be able to see a large enough spectrum smear through the eyepiece to detect absorption lines, etc as they change over a few hours if I point it at Algol for instance?

Or if I had it pointed at some random star during an occultation with the moon or another planet, would I be able to detect by eye the change in spectrum? I mean of course I would eventually want to capture and analyze these spectra digitally at some point, but I want the pleasure of seeing the spectra photons with my own eyes.

Last edited by Siliconaut; 10-27-2018 at 08:59 PM.
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Old 10-28-2018, 10:08 AM   #2
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A diffraction grating might get you something, not sure. But I know that a Fabry-Perot interferometer will definitely give you spectacular spectra.

It works by having light pass through two parallel glass panes that are only slightly transparent - so they act like mirrors. In between the plates, the light reflects multiple times from each pane of glass and destructively interferes away all the unwanted wavelengths, allowing only the wanted one to pass.

The higher the reflectivity of the glass, the more restricted the wavelength is.

Adjusting the distance between the panes allows you to manipulate which wavelength of light passes through the filter, so you can set it to one wavelength, measure the brightness and then set it to another and repeat.
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