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Which camera is better for Spectrometry?

ccd CMOS imaging astrophotography
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#1 odehjas

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Posted 28 October 2020 - 12:37 AM

Hello,

 

I'm new in spectrometry and I'm using Star Analyzer 100. I have ASI224MC and ASI174MM, which one is better for spectrometry? What about ASI462MC and ASI290MM, is any of them could provide better noticeable results and it is worth buying? 

 

Also, what is the recommended gain and offset settings for faint stars spectrometry imaging (hence long exposure), is it HDR (Highest Dynamic Range) or UG (Unity Gain) or LNR (Low Read Noise). Thanks.



#2 robin_astro

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Posted 28 October 2020 - 11:33 AM

Definitely the mono camera for many reasons. The ASI174MM will be fine with the Star Analyser and I would not buy another camera specially for spectroscopy at this stage. If you do decide at some stage to upgrade, the camera will need to match the spectrograph and would likely be cooled for low noise long exposure performance.

 

Spectroscopy is just the same as imaging so the settings that work best for astrophotography will work best there also.  (The biggest issues for beginners starting on bright targets is overexposure and poor focus) What telescope are you using and how far will you be mounting the grating (SA100 or 200?) from the camera. The on line calculator can give guidance. For best resolution increase the spacing until the calculator complains

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

 

Cheers

Robin


Edited by robin_astro, 28 October 2020 - 11:36 AM.


#3 robin_astro

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Posted 28 October 2020 - 11:41 AM

For best resolution increase the spacing until the calculator complains

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

 

 

Or for the faintest objects, reduce the spacing for a shorter more concentrated spectrum but at lower resolution.

 

Robin



#4 odehjas

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Posted 28 October 2020 - 12:32 PM

Definitely the mono camera for many reasons. The ASI174MM will be fine with the Star Analyser and I would not buy another camera specially for spectroscopy at this stage. If you do decide at some stage to upgrade, the camera will need to match the spectrograph and would likely be cooled for low noise long exposure performance.

 

Spectroscopy is just the same as imaging so the settings that work best for astrophotography will work best there also.  (The biggest issues for beginners starting on bright targets is overexposure and poor focus) What telescope are you using and how far will you be mounting the grating (SA100 or 200?) from the camera. The on line calculator can give guidance. For best resolution increase the spacing until the calculator complains

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

 

Cheers

Robin

Many thanks dear Robin. I'm using SA100. I've used the calculator to make sure I have three greens. Attached are the first results I got from my first two observing sessions. The header shows the equipment used. 

 

All of them except one were done by ASI224MC. The ASI174MM is already a cooled version. All the photos are not calibrated for camera response except one of them for Vega. 

 

Once gain thanks for your reply and your advises. 

Attached Thumbnails

  • 3_HIP 107129_Carbon Star_All.jpg
  • 4_HIP 100044 - P Cyg - Blue Hypergiant_Pro.png
  • 7_Scheat_M_Res_Curve_Lines.png
  • Res_Curve_withLin3_Vega_A_es.png
  • Uranus_withLines.png
  • W_Vega_Lines.png
  • W_Vega_No_Lines_Calibrated.png

  • Organic Astrochemist likes this

#5 robin_astro

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Posted 28 October 2020 - 04:15 PM

An interesting comparison. You can see some of the clear advantages of using a mono camera by comparing the uncorrected Vega spectra from the two cameras.

 

The continuum is smoother with the mono camera without the confusing dips produced by the overlap of the response of the  three R,G, B colour filters

 

The colour camera spectrum shows fine scale ripples due to the uneven coverage of the different colour pixels. There are non sensitive pixels in each part of the spectrum; only half of the pixels in the green and only 1/4 of the pixels  In the blue and red regions can detect any light. Because of this the camera is also overall less sensitive than a mono camera. (The effective pixel size is also larger for a colour camera, though in this case it is offset by the smaller pixels in the colour camera)

 

The greater sensitivity of the mono camera, the good size of sensor and the cooling would also make the ASI 174MM  a good choice you decide to upgrade to a higher resolution spectrograph where exposures can be many tens of minutes or even an our or two

 

Cheers

Robin



#6 Organic Astrochemist

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Posted 28 October 2020 - 04:21 PM

Those are a great start at spectroscopy.

Your instrument response seems quite good for a first attempt. One way to evaluate it is to apply the correction to other stars and compare how your spectrum to that of standard reference stars. Preferably these other stars would be close in the sky and at a similar time as your acquisition of Vega.

I’d be interested to hear your experience calculating the instrument response and that of others. There is definitely a learning curve. RSpec is nice because it allows you to see and understand each step, but it would be nice if you could automate the process a little more.

#7 robin_astro

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Posted 28 October 2020 - 07:10 PM


One way to evaluate it is to apply the correction to other stars and compare how your spectrum to that of standard reference stars. Preferably these other stars would be close in the sky and at a similar time as your acquisition of Vega.

I’d be interested to hear your experience calculating the instrument response and that of others. 

I recently added an extra document  to my page of examples of  these sort of standard star tests using both the slitless Star Analyser and the ALPY.

http://www.threehill...troscopy_21.htm

 

It explains the process, going through the steps with some practical tips on how to produce accurately calibrated spectra in relative flux, correcting for instrument response and atmospheric extinction (I tried to make it software neutral as  the steps are essentially the same)

 

Cheers

Robin



#8 odehjas

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Posted 29 October 2020 - 04:56 AM

Thank you Dears for your kind support and replies. 




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