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Sol’Ex - DIY Spectroheliograph

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#1 chantepierre

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Posted 26 January 2021 - 01:11 AM

Hello,
Here’s a link to a (relatively) cheap spectroheliograph a French member of astrosurf.com is currently developing.

Plans and instructions are free and open, with promising results, visible here in French :

http://www.astrosurf.com/solex/

And here is a link that should provide an okay-ish English translation, sadly images seem to not show up in the translated page :

https://gupl5o44hm32...ate.goog/solex/

Have a nice sunny day !
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#2 Astrokhan

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Posted 26 January 2021 - 02:33 AM

Thanks for sharing.

#3 Astrojensen

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Posted 26 January 2021 - 03:53 AM

Wow! I wonder if it would be possible to build a similarly small spectrohelioscope for visual use?

 

 

Clear skies!

Thomas, Denmark



#4 LarsMalmgren

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Posted 26 January 2021 - 10:31 AM

Once again brilliant work by Christian Buil bow.gif bow.gif bow.gif


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#5 mconnelley

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Posted 27 January 2021 - 12:03 AM

Hello:

  This spectroscope won't really work for visual use.  They scan the slit over the sun while taking video, then reconstruct the image in software.  Visually, you'll just see a spectrum of a slice of the solar disk at any given time.  A long time ago I heard of the spectrohelioscope, which uses a rotating pair of slits that sweep over the disk of the Sun, so you get a monochromatic image of the Sun.  You tilt the grating to choose what wavelength to observe.  I've heard that they can work well, but are tricky to get the details right.  

 

Cheers

Mike


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#6 DAVIDG

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Posted 27 January 2021 - 10:19 AM

Wow! I wonder if it would be possible to build a similarly small spectrohelioscope for visual use?

 

 

Clear skies!

Thomas, Denmark

 Yes it has been done. There was article back in the 70's in Sky and Telescope were a high school student build  a small spectrohelioscope  that used two moving slits and an inexpensive transmission grating to make one. It was attached to a his 60mm refractor. The issue with a small instruments is the spectral resolution which determines the bandpass. With short focal length optics the width of the spectral lines is very narrow. So the slits required are also very narrow, the result is that you have a dim image and the band pass is fairly wide.  Visual spectrohelioscopes require optics with focal lengths of many feet. The Hale spectrohelioscope I restored that is installed at Stellafane has optics in the spectroscope section that have  a focal lengths of 13 feet ! That makes the spectral lines wide and now you close down the slits to be narrower then the  full width of the lines which narrows the bandpass to be sub angstrom in width.  The result is you see the Sun with a bandpass in H alpha between 0.7 to around 0.3 angstrom just by narrowing the exit slit. 

   The reason why these small spectroheliograph work is that your using a CCD camera to image the spectrum and the CCD has very small pixels and you can vary the exposure .  You allow the Sun to drift over the entrance slit of the spectroscope and record a video of the spectrum centered on the wavelength you want. Then you post process the video, cutting out only the image of the spectral lines you want and then stacking them next to each other to form the 2D image. The focal length of the optics in the spectroscope section is designed so the spectral lines is a  couple of pixels wide. Since the pixels are only a few um wide the spectral lines doesn't have to be by wide to cover a couple of them. You post process the image and cut out the image of the spectral line you want but  you don't  use the full width the lines but a narrower width. That narrower width defines the band pass so you can achieve  a sub-angstrom band pass. The key is the CCD has pixels small enough that the spectral line doesn't need to be  magnified by long focal length optics. So you can have a small instrument like what is described in the Buil's website. 

 

                 - Dave 



#7 Chuck Hards

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Posted 27 January 2021 - 11:53 AM

Dave, I think you are remembering Jack Newton's article in S&T back in the 70's.  Jack wasn't yet a household name in this country back then but was in his building heyday and was already a young man raising a family, and known to most RASC members of the day.

 

I accumulated most of the parts to build his spectrohelioscope but never finished it.  I still might if and when I ever retire.



#8 DAVIDG

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Posted 27 January 2021 - 12:21 PM

 Jack Newton's device  is not s spectrohelioscope  but a solar prominence spectroscope. Here is link to some images taken with this type of device 

https://www.cloudyni.../#entry10288178  In  a solar prominence  spectroscope you center up the H-alpha line  which you see as a dark line on a red background. You place the limb of the Sun on the entrance slit of the scope scope and scan around the limb. Any place there is  a prominence you will see a red "knot" in the black line. You slowly open the slit and you'll be able to see the prominence. If too large it won't fit in the slit width and if you open the slit more to see it the contrast goes way down and it will disappear. The reason why you can see the prominence is that is acts like it own slit and is narrower enough to cause a sub angstrom view for the body of the prominence . The background light is suppressed because the slit on the spectroscope is not very wide so the total bandpass is around a few angstrom.

   This type of setup will not work for visual images of the surface thou. You need the design of spectrohelioscope or a modern day sub angstrom  filter. If your were to take the Newton's design and couple it with a CCD camera you would have a spectroheliograph very similar to what Buil is doing in his design and you can get the same results to make 2D images of the Sun in various wavelengths.

 

                  - Dave 



#9 EJN

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Posted 27 January 2021 - 12:21 PM

I remember the Jack Newton article, it was a spectroscope. He would place the slit on the solar limb and open the slit, and you could see prominences within the widened H-alpha line.

I also remember the compact spectrohelioscope, that was someone else, I'll have to search to see if I can find the author's name.

The compact spectrohelioscope had a resolution limited to about 30 arc seconds due to the short focal length.


Edited by EJN, 27 January 2021 - 12:32 PM.


#10 EJN

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Posted 27 January 2021 - 12:31 PM

Found it in the S&T index:

 

1971 10(Oct) p.238 - Gleanings for ATMs "A Compact Prizewinning Spectrohelioscope" "Horne, Clifton"

 

 

There was also an article by Fred Veio on a spectrohelioscope with rotating slits S&T Jan. 1969, and a professional-level one built by Walter Semereau S&T Nov. 1967


Edited by EJN, 27 January 2021 - 12:50 PM.


#11 PEterW

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Posted 28 January 2021 - 09:43 AM

Not a huge meter long monster.... very interested in reading this one. I was thinking about a compact and cheap spectroscope for looking at the spectrum detail.

Peter

#12 DAVIDG

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Posted 28 January 2021 - 10:14 AM

 There is great book on how to build and use these devices by Ken Harrison  " Imaging Sunlight Using a Digital Spectroheliograph"

 

                   - Dave 



#13 PEterW

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Posted 29 January 2021 - 02:44 AM

I’ll start making a shopping by list of parts, this looks very useful and can be used as a spectroscope with an eyepiece.

Peter

#14 don clement

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Posted 30 January 2021 - 12:49 AM

Once again brilliant work by Christian Buil bow.gif bow.gif bow.gif

I have his book on CCD astronomy from WB. https://www.biblio.c...phoCVwgQAvD_BwE

 

Don




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