Building a basic spectroheliograph

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taratasy
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Building a basic spectroheliograph

Post by taratasy » Mon Jul 04, 2016 9:37 pm

Greetings everyone !

I am a geology student and long-time astronomy enthusiast. I grew a strong interest in observing and imaging the sun, now with my faithful lunt LS50THa. The h-alpha line is marvelous ! Everyday I check the GONG H-alpha monitor in hope to see an odd-looking prominence and twisted filaments.
Recently I fell in love with the Ca-K line :oops: thanks to many images posted on the net ; unfortunately I can't afford any new expensive equipement to image it and fullfill my passion.

Then, I learned about the spectroheliograph. Man, what a fine piece of instrument !
Being able to image the sun in ANY visible wavelenght is outstanding, it sure caught my attention.
I found this web page http://www.astrosurf.com/cieldelabrie/sphelio.en.htm which made me think that I could possibly build one myself ! I am no expert in optic and DIY but I am a quick learner and enthusiastic.

I found many websites such as http://www.astrosurf.com/spectrohelio/index-en.php which helped me a lot to understand the theory of spectroheliography.
In the end the construction of an amateur spectroheliograph seems fairly difficults with many mathematics and optical elements involved such as the telescope, the collimator, the camera lens, the sensor, the grating, the slit... But it doesn't scare me and I have all the time I need.

However I dont think I could do it all by my own, therefor I registered in Solarchat and posted here in hope to get comments and advice from you all :D

For recap, I would like to build a small spectroheliograph prototype that will do the trick, not necessarily an high quality construction.
At this point I own some elements that might be usefull for the construction :

- a webcam creative live ultra with a ICX098AK CCD sensor (1/4" and 5.6μm pixel size)
- a 500mm/f8 mirror telephoto lens
- a 135mm/f2.8 macro lens
- a 50mm/f1.8 lens

However I am not very sure if I can obtain enough spectral resolution (or dispersion ???) with those optics. I would at least get some proms in h-alpha.. (that means I need to get ~0.8 angstrom per pixels right ?).
I need to make some calculation but I lack some informations. Fortunately I will receive the book "Imaging Sunlight Using a Digital Spectroheliograph" shortly, It will surely provide everything I need :)

I considered to build a Y-shapped instrument similar to this one http://www.astrosurf.com/buil/us/stage/calcul/spec.jpg as it seems to be the easiest to assemble.

So, that is where I am ! I hope you don't find my idea too farfetched :)

Looking forward to reading from you all.

Taratasy

PS : I use google translat occasionally, forgive me if some sentences are weird.

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Re: Building a basic spectroheliograph

Post by Merlin66 » Tue Jul 05, 2016 8:48 am

Welcome on board, mate!
There are a few members who have already built their SHG's and I'm sure will be ready to assist.
When you read the book I'm sure everything will be much clearer.
I also have a spreadsheet which will assist you to validate your design and estimate the performance.
It's currently available over on the files area of the Astronomical Spectroscopy group - look for SimSpec SHG. If you have problems drop me a PM or email for a copy.
Other than the fast frame camera (mono preferred) there are only three things to build and assemble:
The telescope
The entrance slit
and the spectrograph.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Building a basic spectroheliograph

Post by taratasy » Tue Jul 05, 2016 11:49 pm

Thanks Merlin, the spreadsheet and the book are a great help !

I think I found a viable SHG configuration using the elements I mentioned above :

- I will use the 50mm/F8 mirror lens with a barlow x2 as the telescope (1000mm focal lenght in total)
- The 135mm/f2.8 macro lens will be the collimator and the 50mm/f1.8 lens will be the camera lens
- I will use a 12.5x25mm reflection grating at 2400 grooves/mm
Now, the collimator/camera angle would be 20° and the camera/grating distance 120mm
Considering the lenses dimension and d1, everything should fit together whithout any problem !

In the end :
- The sun height should cover almost all the sensor's length.
- Spectral resolution at 6563 Å : 0,95 Å (Not as much as I wanted but hey, you can't achieve miracles with so little to beggin with). It will be enough for Ca-K though.

Well I find all of that very exciting, I hope it works in practice !

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Re: Building a basic spectroheliograph

Post by Merlin66 » Wed Jul 06, 2016 3:34 pm

Tara(?)
Caution.....
With no ERF etc. the mirror lens may not be a good choice for the telescope, the build up of the solar energy on the secondary mirror/ corrector may give problems.
A cheap and cheerful 60/900 achromatic refractor would achieve the same job.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Mon Jul 11, 2016 5:05 pm

I got a 50/500mm (f10) achromatic and redesigned the whole construction, things got wayyy easier :) !

But I have a little concern : I need to use a collimator with 200mm focal length, fortunately I own a small telescope finder 50/200mm (f4) which would do the job. However the SHG spreadsheet tell me that my collimator must work at f10. Can I just put an opaque mask with a 20mm hole in front of the lens to achieve the correcte aperture/focal ratio or should I get a real 200mm length f10 lens at SurplusShed or any 200mm telephoto-lens with a f10 stop ?

EDIT : in the book, chapter 7.1, it says as an exemple that the apperture of the lens should be stopped down if the focal ratio is smaller than the telescope's one. Well I guess I will simply use an opaque mask. :mrgreen:

Many thanks.

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Re: Building a basic spectroheliograph

Post by Merlin66 » Mon Jul 11, 2016 7:15 pm

Tara,
No real need to fit a physical aperture stop to the collimator....
The incoming f10 beam from the telescope through the entrance slit will automatically generate a f10 beam at the collimator and act as an aperture stop.
Hope this helps.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Sun Jul 17, 2016 10:21 pm

Although I waiting for my diffraction grating, it does not stop me from using my setup :

Quick shot of the moon :
hourq.jpg
hourq.jpg (41.25 KiB) Viewed 3704 times
The slit made from two razor blade seems to work ! Focusing is a bit harsh but I will surely get better at it.

Next step : The Sun !
More to come in two or three weeks :D

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Re: Building a basic spectroheliograph

Post by highfnum » Sun Jul 17, 2016 10:45 pm

hey another moon image!!

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Re: Building a basic spectroheliograph

Post by taratasy » Sat Aug 06, 2016 5:05 pm

My SHG is almost finished ! I made a try today, I can see clearly the spectral lines with my webcam.
I tried to take a picture in CaK but the result is pretty bad :
derp.jpg
derp.jpg (14.32 KiB) Viewed 3602 times
I find it pretty difficult to have the sun on focus on the slit, is there a way to tell or do we have to guess and try ?
Plus my slit is dusty..

I should greatly improve in the next few days.

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Re: Building a basic spectroheliograph

Post by marktownley » Sat Aug 06, 2016 7:40 pm

You're getting there!
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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Re: Building a basic spectroheliograph

Post by Merlin66 » Sat Aug 06, 2016 10:28 pm

Slit focus - a bit of trial and error.
Look at the limb of your image - it's not crisp and tight - this should be as clear and crisp as possible.
(See "Imaging Sunlight", p143)
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Sun Aug 07, 2016 3:13 pm

Almost there !

Ha
16_17_56d_000 - copie.jpg
16_17_56d_000 - copie.jpg (72.66 KiB) Viewed 3573 times
CaK
16_57_33_000 - copie.png
16_57_33_000 - copie.png (565.24 KiB) Viewed 3573 times

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Re: Building a basic spectroheliograph

Post by highfnum » Sun Aug 07, 2016 6:20 pm

getting there

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Re: Building a basic spectroheliograph

Post by Merlin66 » Sun Aug 07, 2016 10:15 pm

Do you know what slit gap you're using?
Just needs a little more practice......
Onwards and Upwards.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Building a basic spectroheliograph

Post by taratasy » Sun Aug 07, 2016 10:22 pm

Merlin66 wrote:Do you know what slit gap you're using?
No I don't, I tried to make the gap the thinnest possible by eye. Now I got a laser pointer so I will get the right width.

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Re: Building a basic spectroheliograph

Post by Merlin66 » Sun Aug 07, 2016 10:43 pm

I think the colour webcam chip will become an issue...
The size of the solar image v's chip size I think will need a bit more processing.
All in all you're doing well....keep it up.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Sun Aug 07, 2016 10:48 pm

Thanks, I keep you updated.
I will soon get a Zwo ASI120MM-S mono !

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Re: Building a basic spectroheliograph

Post by Merlin66 » Sun Aug 07, 2016 11:09 pm

Sounds good!
Next time upload a couple of images of your SHG, it will be interesting to others....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Building a basic spectroheliograph

Post by Montana » Mon Aug 08, 2016 10:59 am

I think the camera may be causing a few problems but it is working, I see proms and plage :hamster:

Alexandra

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Mon Aug 08, 2016 4:53 pm

Here is the beast :

IMG_6875 - copie.jpg
IMG_6875 - copie.jpg (123.23 KiB) Viewed 3520 times
IMG_6876 - copie 2.jpg
IMG_6876 - copie 2.jpg (122.6 KiB) Viewed 3520 times
IMG_6877 - copie.jpg
IMG_6877 - copie.jpg (151.03 KiB) Viewed 3520 times
It is not a work of art.
The telescope and collimator are held in place by two sets of 3 screws mounted on PVC tubes, it greatly helps to align the optics.
The camera lens is held in place by... rubber band. This is the best I can do for the moment but it works well.
The diffraction grating is glued on a wood piece, which is glued on a rotative platform made of an old lens cap.

There is several things I need to improve :

- Find another way to held the grating on the platform
- Find another way to held the camera lens
- Protect the whole thing from parasitic lights
- I need to align correctly all the optical components, it is kind of wonky at the moment (as you can see in the third pic).

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Re: Building a basic spectroheliograph

Post by Merlin66 » Mon Aug 08, 2016 10:02 pm

Looks promising!
I'd suggest a couple of rings to support and align the camera lens similar to the ones you use on the telescope/ collimator.
You can use a laser collimator to align all the optics and grating. Just mount it central and square to the telescope objective....
Place a wire (ex coathanger?) loop over the grating area and then drape the instrument with a black cloth to reduce the parasitic light.
(I don't see the blaze arrow on the top of the grating??? This arrow should point towards the imaging lens.)
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Tue Aug 09, 2016 8:56 am

Thanks for the tips !
The arrow is present but it does not appear on the photo I don't know why.

I am worrying because vertical lines started to appear on the grating. I manipulate it with great care so I don't really understand what causes this.

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Re: Building a basic spectroheliograph

Post by Merlin66 » Tue Aug 09, 2016 9:05 am

Taratasy,
Can you explain further??
Are you seeing "defects" in the grating surface??
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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taratasy
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Re: Building a basic spectroheliograph

Post by taratasy » Tue Aug 09, 2016 9:44 am

I bought it from edmund optics, optometrics was out of stock at the time. It was clean and without defects when I unboxed it.

Here is a picture : I first noticed those lines when they where smaller than that, the next day they had grown in lenght and number. Fortunately they seem to have stopped !
IMG_6879 - copie.jpg
IMG_6879 - copie.jpg (148.55 KiB) Viewed 3492 times

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Re: Building a basic spectroheliograph

Post by Merlin66 » Wed Aug 10, 2016 6:05 am

Hmmm
Yes, I've seen similar grating faults...usually they do not have a major impact on the performance and can be caused during the manufacture of the grating.
It's unusual to see them change over time...
The epoxy substrate may be causing the problem, but as I say, it's not something I've seen before.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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