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Budget spectroscopy for beginner?

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#1 Tom Stock

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Posted 05 December 2019 - 09:12 PM

So I was cruising around on eBay a few weeks ago and stumbled across 100 line/mm gratings for $5.

 

I've always been interested in trying spectroscopy but at the moment I really can't afford to invest $300 into it, so I figured what the heck and I purchased one. 

 

I received my grating cut it down and slipped it into an old 1.25" filter ring.

 

I purchased the book "Astronomical Spectroscopy for Amateurs" and it discusses software called "VSpec", but haven't really had a chance to dig into it yet.

 

I also found IRIS and ISIS, which both run on my mac under wine.

 

ISIS refuses to open my color fits files for some reason. IRIS seems to work but I have a steep learning curve to get through.  I have not tried VSpec yet (Virtualbox).

 

The image of polaris was taken using a C5 using a ASI120MC just to test the grating.

 

Does this look like it will be useable? Probably a dumb question, but like I said I haven't had time to really start reading yet.

 

EDIT: After some reading it looks like the spectra is out of focus for starters.

 

Is anyone still using older programs like IRIS or VSpec?

 

Thanks

POLARIS-201005.png


Edited by Tom Stock, 05 December 2019 - 10:24 PM.

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#2 robin_astro

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Posted 06 December 2019 - 09:15 AM

Hi Tom,

 

I still use both for certain jobs. Visual Spec is still a current program but ISIS has superseded IRIS for spectroscopy

You can still use IRIS and Visual spec to process your spectra following the instructions here on my website

http://www.threehill...roscopy_11a.htm

(The first step is to remove the colour information to produce a mono image that Vspec will accept)

 

Your inexpensive grating will probably not be very efficient compared with the Paton Hawksley Star Analyser for example (with most  grating film much of the light ends up going straight through instead of into the spectrum you want) but you should be able to get some good spectra of some bright stars. (Focus on the features in the spectrum, not the zero order.) It looks like you are using an achromatic refractor which is making the spectrum out of focus at the blue end so best focus will be a compromise.  Have a look at the Star Analyser instructions which will give you some more hints and tips

https://www.patonhaw...y.com/resources

 

Cheers

Robin

 

EDIT: I see you are using a C5. SCT are  normally free of chromatic aberrations. Are you using a focal reducer? That might explain the out of focus "fishtail"effect in the blue. If not, focusing further towards the blue end looking for the Hydrogen  Balmer H beta line chosing a hot main sequence star might help. (polaris is not a good starter target as it does not have any strong distinct features in the spectrum)


Edited by robin_astro, 06 December 2019 - 09:33 AM.

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#3 Tom Stock

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Posted 06 December 2019 - 11:04 AM

Hi Tom,

 

I still use both for certain jobs. Visual Spec is still a current program but ISIS has superseded IRIS for spectroscopy  .....

 

(quote trimmed)

Hi Robin, I've actually seen your website before, thanks for sharing that again. At one point I had printed it out and placed it into my "all things astronomy" binder (which I will dig out now) but completely forgot about it until you shared the link. That is perfect thanks.

 

I was using an F6.3 focal reducer, as you mentioned.

 

I will try again without the reducer, and will select a better star, and focus on the spectrum not the zero order. 

 

Thank you!

Tom


Edited by Tom Stock, 06 December 2019 - 11:06 AM.


#4 Tom Stock

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Posted 06 December 2019 - 07:37 PM

Ok after reading links provided by Robin, and digging into my book, I was able to get my (very poor) spectrum of polaris into VSpec and compare against various types (such as F8V). This is not good data but the curve was actually recognizable compared to other curves I've seen of polaris so that was surprising.  This was only an exercise to learn the basic process. Figured out how to correct using camera response curve, etc.

 

The beginning steps are not as complicated as it first seemed.

 

It is clear now why the Star Analyzer is so popular. Not only because it's easy, but because it's efficiency is very good.  I would expect my poor DIY grating to have 1st order efficiency as low as 5% - 10%. 

 

But it's a great introduction to the hobby for nearly free. Very excited to use it tonight.


Edited by Tom Stock, 06 December 2019 - 07:38 PM.


#5 Rankinstudio

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Posted 08 December 2019 - 02:03 AM

Same boat. Looking at a good 2" filter recommendation for spectra. I'm mostly interested in obtaining spectra of comets.

 

Using a 12" F4 OTA with Atik 428exm.

 

Thanks!



#6 robin_astro

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Posted 08 December 2019 - 10:14 AM

Same boat. Looking at a good 2" filter recommendation for spectra. I'm mostly interested in obtaining spectra of comets.

 

Using a 12" F4 OTA with Atik 428exm.

 

Thanks!

With a simple slitless grating spectrograph the target has to appear approximately stellar in the image (ie the size of the image of the target must be small relative to the length of the spectrum otherwise the spectrum is blurred). Will the comets you plan to measure fit this criterion ? If not you will need either to use a slit spectrograph or use a grating mounted in front of a camera lens (an objective grating setup) as here on my website for R1 2012 Lovejoy 

http://www.threehill...troscopy_17.htm

I am not aware of any 2 inch diameter gratings available commercially but if you plan to use it after the telescope then a standard 1.25 inch grating eg Star Analyser works provided you place the target in the unvignetted region. (The spectrum will not be vignetted as the dispersion is after the grating) There are various solutions to mounting a Star Analyser in a 2 inch system for example using a blank 2 inch filter cell and the mounting kit Paton Hawksley supply for the Star Analyser

http://www.threehill...00_mounting_kit

 

Cheers

Robin


Edited by robin_astro, 08 December 2019 - 10:16 AM.

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#7 Rankinstudio

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Posted 08 December 2019 - 05:12 PM

Thanks for the info Robin.



#8 Ron359

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Posted 30 December 2019 - 03:49 PM

This calculator link seems to be out of date:    https://www.patonhaw....com/calculator

 

Is the SA 200 available in the U.S.?   thanks.   



#9 robin_astro

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Posted 30 December 2019 - 07:17 PM

This calculator link seems to be out of date:    https://www.patonhaw....com/calculator

 

Is the SA 200 available in the U.S.?   thanks.   

The Star Analyser manufacturer Paton Hawksley's  pages

https://www.patonhaw...e/star-analyser

https://www.patonhaw...ar-analyser-200

now link to the version of the calculator on the RSpec-astro website

https://www.rspec-as...com/calculator/

The Star Analysers are available from RSpec-astro in the US or direct from Paton Hawksley

 

Cheers

Robin


Edited by robin_astro, 30 December 2019 - 07:21 PM.

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#10 Rich (RLTYS)

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Posted 01 January 2020 - 09:24 AM

Is "Rainbow Optics" still around? They used to sell inexpensive Spectroscopes both visual and imaging.




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