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Old 27-08-2021, 08:24 AM
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Merlin66 (Ken)
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Mini SHG First images!

I've been working on a "Mini SHG", following the SolEx 3D printed concept by Christian Buil.
http://www.astrosurf.com/solex/sol-e...tation-en.html


In my case $2 lenses from Surplus Shed and 3mm MDF housing.
Using a 2400 l/mm grating, 19 micron slit gap and an ASI 178 camera. FireCapture at 350 fps.
Initial trials have been hampered by the weather, but early images look very promising.
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Old 27-08-2021, 08:59 AM
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Very interesting
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Old 27-08-2021, 09:06 AM
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Merlin66 (Ken)
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Thanks mate!
With evolution of the supporting software it won't be long before we have "LiveView" SHG imaging.


A very, very cost effective way to image the Sun in any visible wavelength.
I canvassed the SHG as a platform for solar imaging some ten years ago, and now the technology has finally caught up.....
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Old 27-08-2021, 09:18 AM
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Fascinating. Gotta read this tonight in details. Thanks for posting.
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Old 27-08-2021, 09:44 AM
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Did a little clean up in Registax6 and compared to the GONG image....
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Old 27-08-2021, 10:01 AM
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Quote:
Originally Posted by Merlin66 View Post
Did a little clean up in Registax6 and compared to the GONG image....
That's a match.
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Old 27-08-2021, 10:15 AM
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Quote:
Originally Posted by Merlin66 View Post
Did a little clean up in Registax6 and compared to the GONG image....
Excellent.

Your image is a bit blurry in direction of Sun movement (and perpendicular to slit orientation) as expected, but that can be improved..
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Old 27-08-2021, 10:23 AM
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Awesome Ken!!
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Old 27-08-2021, 10:28 AM
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Bojan,
I agree, room for improvement.


This image was based on a 18sec scan in Dec and a frame rate of only 40 fps.
I've now found the problem with the frame rate and can now get >300 fps.
I think that, and better focus, will improve the next round of images.
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Old 27-08-2021, 10:59 AM
Saturnine (Jeff)
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Thanks for posting this Ken, certainly piques the interest, an enjoyable read and a fascinating project. The results speak for themselves but unfortunately I doubt I will have the time or 3D printer to make the parts.
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Old 27-08-2021, 11:17 AM
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Yeah,
I don't have a 3D printer either, and I do have some concerns about "plastic" solar instruments.
The Mini SHG was assembled from commercial bits and pieces in the junk box and the housing made from 3mm MDF and some 6mm ply.
I'm using Surplus Shed lenses (10 for $5 !!!) (I have some spare if you want to trial them), the Custom slit plate and grating holder which were "spares" for the Spectra-L200. The helical imager focuser was ex eBay.
I think probably all up for parts, say, $600.
It's used with an ED80 stopped down to 60mm.


It's becoming a serious contender against Lunt and Coronado etalon filters which cost thousands $$$$$$.


One of the French guys, Jean-Francois Pittet, with a Bresser 102/1000 telescope and the SolEx achieved this image - no additional processing other than through INTI:
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Old 27-08-2021, 11:25 AM
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Quote:
Originally Posted by Merlin66 View Post
It's becoming a serious contender against Lunt and Coronado etalon filters which cost thousands $$$$$$.
This is the main motivation for me too. Apart from the fact I like tinkering with stuff too.
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Old 27-08-2021, 11:44 AM
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Awesome work Ken , look forward to progress on the project ….. will have to read up on your book about SHGs https://www.bookdepository.com/Imagi.../9783319248721
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Old 27-08-2021, 11:55 AM
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Fascinating!
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Old 27-08-2021, 11:57 AM
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BTW..

Quite some time ago I was playing with idea to use scanner linear CCD chip (I have couple of them in my drawers) instead of camera for something like this.
Idea came from this paper: https://www.google.com/url?sa=t&rct=...hWHW8f7i3UAXiY

Another one: https://hackaday.com/tag/linear-ccd/

I am guessing with Arduino to drive it, it wouldn't be a big problem to assemble working prototype... perhaps the frame rate (or line-rate) may be the issue here so STM32 would be better...

Last edited by bojan; 27-08-2021 at 12:21 PM.
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Old 27-08-2021, 12:01 PM
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could winjupos assist with the blur?
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Old 27-08-2021, 12:54 PM
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Bojan,
A couple of amateurs have tried using a linear array.
It turned out not too successful.
The shape of the spectral lines - tilt, slant, smile, make it very difficult to accurately position the array.
Also the need for very fast frame rates (>150fps) and very small pixels (+/- 3 micron) when using a small SHG like the SolEx or Mini SHG really mean that the current CMOS cameras like the ASI 178 are capable of doing a great job.


Russell,
The distortions you see are due to the scanning rate combined with the sampling ratio and pixel size.
All these variables can be improved. The INTI software already does some fancy foot work in preparing the circular image outcome and removing transversalium (dark lines due to dust on the slit).
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Old 27-08-2021, 02:20 PM
Eris (Gerard)
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Brilliant concept Ken. I'm sure the images will improve as you master the hardware. Congratulations.
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Old 27-08-2021, 04:53 PM
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Gerard et al,
Thanks for the comments and feedback.
I have a few SHG but they, relative to the “miniSHG”, are very large and difficult to mount on the available HEQ5.
The Mini version weighs next to nix, and can easily fit/ work on small refractors and is therefore more useable and easier to use.
The new software INTI is a revolutionary step forward, it allows fantastic quick processing of the videos, and has completely changed the attitudes towards the traditional SHG.
Ken
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