Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

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Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

I woke up early to try to do some solar imaging here in London before the heat became unbearable. I was able to get some nice CaH images, but by the time I got to H-alpha and the Ca-IR line (at 8542 angstroms), it was already getting pretty steamy and I think the resolution decreased as a result. Here is a mosaic of full disks:

Ca-H (left), H-alpha (centre) and Ca-IR [854.2nm] (right). All taken at 480mm focal length, 80mm aperture. H-alpha taken with 2400 l/mm grating, other two with 1800 l/mm.
Ca-H (left), H-alpha (centre) and Ca-IR [854.2nm] (right). All taken at 480mm focal length, 80mm aperture. H-alpha taken with 2400 l/mm grating, other two with 1800 l/mm.
190722-Ha-Ca-480mm.jpg (912.84 KiB) Viewed 989 times


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

Below are closeups (100% crop) of the two Calcium lines (UV and IR):

Close up of the Ca-H image.
Close up of the Ca-H image.
190722-CaH-480mm-1800g_crop.jpg (722 KiB) Viewed 971 times

Close up of the Ca (854.2nm) image.
Close up of the Ca (854.2nm) image.
190722-CaIR-480mm-1800g_crop.jpg (499.39 KiB) Viewed 971 times

The 1800 l/mm grating combined with an 80mm aperture refractor seems to give nice results with the CaH line at 396.8nm.

The Calcium line at 854.2nm (in the IR) is interesting but from my experiments with a small telescope, it doesn't seem to offer much over the more traditional imaging lines.

All images were taken in the morning of July 19.
Last edited by thesmiths on Fri Oct 14, 2022 3:03 pm, edited 1 time in total.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by Valery »

Thanks, Douglas.

Very interesting. We need to keep in mind that angular resolution at 854nm is more than 2x less vs resolution at 393nm.
We can see that at 854nm the "surface" of the sun is very different to what we see at 393nm and very much like at 656nm Ha, but with lower resolution and contrast.

Can you try to image at 854nm with a larger telescope? May be 150mm?


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by p_zetner »

The hydrogen alpha is superb as always and the CaH is your best result yet.

In my opinion, the infrared Ca lacks contrast in that the chromospheric network is poorly visible. I don’t think this is due to any inherent difference in UV vs IR calcium chromospheres but points to a lack of contrast and spatial resolution in your IR imaging. In my first attempt at imaging the Ca triplet ( https://solarchatforum.com/viewtopic.php?t=29064 ) , I found the CaH, CaK and the Ca 849.8nm lines all gave remarkably similar results. Any “hybrid” hydrogen / calcium appearance that you might expect will likely only be discernible at high spatial resolution.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

p_zetner wrote: Wed Jul 20, 2022 1:16 am In my opinion, the infrared Ca lacks contrast in that the chromospheric network is poorly visible. I don’t think this is due to any inherent difference in UV vs IR calcium chromospheres but points to a lack of contrast and spatial resolution in your IR imaging. In my first attempt at imaging the Ca triplet ( https://solarchatforum.com/viewtopic.php?t=29064 ), I found the CaH, CaK and the Ca 849.8nm lines all gave remarkably similar results. Any “hybrid” hydrogen / calcium appearance that you might expect will likely only be discernible at high spatial resolution.
I didn't see the kind of contrast I expected at 854.2nm. The line does look qualitatively different than the 849.8nm line you imaged so there might be differences. With 1800 l/mm grating, I first did CaH then afterward gave 854.2nm a try. The wavelengths are so different that everything had to be refocused and maybe I did not get that quite right. With Ca-H/K, there are so many very high contrast features that focusing is easier.

I might next time try imaging all three lines of the Calcium triplet. My guess is they will not show exactly the same thing and I think there is a reason, as suggested by Valery, that 854.2 nm might be different. Since all three are close in wavelength, not too much refocusing would be required.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

Valery wrote: Tue Jul 19, 2022 10:39 pm We can see that at 854nm the "surface" of the sun is very different to what we see at 393nm and very much like at 656nm Ha, but with lower resolution and contrast. Can you try to image at 854nm with a larger telescope? May be 150mm?
Hi Valery, is it known that the three lines of the IR Calcium triplet behave differently? The two Ca-K/H lines do not behave noticeably different for imaging. You seem to suggest that the 854nm line is unique in some way (while Peter Zetner hypothesised that they should act the same as Ca-K/H).

With regards to larger aperture, the biggest I have access to is really 106mm. This gives quite good results for H-alpha but of course will give worse resolution for the even longer wavelength. I use the equipment with no ERF at all and it is actually fine for 106mm aperture. The one time I tried with a 140mm aperture, I noticed some damage was done to the slit (fortunately, I had a lot of them made). That telescope has a quite short focal length (f5.7) as it is a Petzval design. This makes the intensity even higher as the Sun's projected image is actually smaller than with my 106mm refractor (which is around f6.5). In addition, I have heard from others that these complex optical designs are not very good for this kind of work (more suited for night time).


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

p_zetner wrote: Wed Jul 20, 2022 1:16 am the CaH is your best result yet.
The CaH did turn out much sharper than previous efforts. Maybe it was because it was very early morning. Perhaps the 1800 l/mm grating gives good contrast on this image scale. The 80mm f6 APO might also be working well at this wavelength. I'll also post the full disk image here.

CaH SHG. 480mm focal length, 80mm aperture. 1800 l/mm grating.
CaH SHG. 480mm focal length, 80mm aperture. 1800 l/mm grating.
190722-CaH-480mm-1800g.jpg (1.13 MiB) Viewed 903 times

Note that versus our previous 700mm focal length images, the 480mm telescope gives a small enough projection on the slit that the image is in quite good focus across the whole disk. At 700mm, we have to chose which area we want to be in focus.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by Valery »

Douglas,

I really don't know if there any difference between lines in the IR triplet. I can only say that professional astronomers have reasons to choose this 854nm line.

May be this line scan will be interesting to see the changes in surface appearance with CWL position changes. CWL changes in pikometers (0.01A).

Valery
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_IBIS scan in pikometers (0,01A) 2 crop.gif (1.45 MiB) Viewed 895 times


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by Carbon60 »

Superb work, Douglas. Inspirational!

Stu.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by Montana »

A super comparison Douglas :bow :hamster: my first thoughts when viewing the images are that your system is optimised for CaK and Halpha extremely well, when going to the far infra red it seems the resolution goes down. I was wondering whether it would not be possible to get this wavelength in high resolution in this system with the wavelength being so long. I have very limited understanding but at work when we use FTIR imaging it is impossible to get high resolution as the wavelength is too long (diffraction limited).

Alexandra


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

Montana wrote: Thu Jul 21, 2022 7:15 am My first thoughts when viewing the images are that your system is optimised for CaK and H-alpha extremely well, when going to the far infrared it seems the resolution goes down. I was wondering whether it would not be possible to get this wavelength in high resolution with this system with the wavelength being so long. I have very limited understanding but at work when we use FTIR imaging it is impossible to get high resolution as the wavelength is too long (diffraction limited).
Yes, the difference in wavelength between Ca-H and the IR is a factor of 2.15, but from H-alpha to the IR is only a factor of 1.30. But it could be that the optics are not built to focus well in the infrared. The fact that the optics, in particular the 80mm APO triplet, does so well near the UV, might mean that the performance falls off in the IR.

Or it might just be that I did not do a good job in focusing in the IR. The contrast is lower, which makes focusing harder.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by Valery »

thesmiths wrote: Thu Jul 21, 2022 1:58 pm The fact that the optics, in particular the 80mm APO triplet, does so well near the UV, might mean that the performance falls off in the IR.

Or it might just be that I did not do a good job in focusing in the IR. The contrast is lower, which makes focusing harder.
Can you, please, tell me is this 80mm telescope doublet or triplet?

What is the 106mm telescope?

I will look in Zemax how both these scope may behave at 854nm/



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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by thesmiths »

Valery wrote: Thu Jul 21, 2022 4:44 pm Can you, please, tell me is this 80mm telescope doublet or triplet? What is the 106mm telescope?
I will look in Zemax how both these scope may behave at 854nm.
Both are triplet. The 80mm f6 is from LOMO (sourced by APM). I actually have not used it so much for solar. It seems to be ok at Ca-H and H-alpha.

The 106mm I think was built by LZOS. I measured the focal length at about 700mm. I have used this one from Calcium-K to Baader continuum to H-alpha and it is very sharp at all three wavelengths. It gives a really perfect star test.


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Re: Full-disk SHG images at 656.3nm, 396.8nm and 854.2nm

Post by marktownley »

I love the discussion and detail that evolves in these threads! Thanks all!


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