CaH and H-beta full-disk SHG images -- good resolution, July 29

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CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by thesmiths »

We tried our new SHG setup (see viewtopic.php?t=37284) this morning (July 29). The Ca-H turned out very well, as did H-beta. The H-alpha was not as pleasing as hoped for, but the solar disk is at the moment somewhat featureless at that wavelength, at least compared to the dynamism of the last few weeks.

For Ca-H, we used a 72mm aperture mask on our APO triplet refractor (106mm, 720mm), which brought the telescope to f10. The following image is a stack of 13 frames (AS3!), imppg, and Photoshop. There is a lot of surface structure so it's best viewed at full scale (open image in new tab).

CaH SHG image, 72mm aperture, f10. 2400 l/mm grating, 9 micron wide slit. Stack of 13.
CaH SHG image, 72mm aperture, f10. 2400 l/mm grating, 9 micron wide slit. Stack of 13.
290722-CaH-720mm-72mm-2400g-stack-13_crop.jpg (1.85 MiB) Viewed 1148 times

The H-beta was taken without the aperture mask, so 106mm at f6.8. This was a stack of 14 frames. Again, there are a lot of fine details so it's best viewed at full scale (open image in new tab). If you toggle between the two open tabs of Ca-H and H-beta, you can better compare the corresponding features.

H-beta SHG image, 106mm aperture, f6.8. 2400 l/mm grating, stack of 14.
H-beta SHG image, 106mm aperture, f6.8. 2400 l/mm grating, stack of 14.
290722-Hb-720mm-2400-stack-14_crop.jpg (1.92 MiB) Viewed 1148 times

As mentioned above, the H-alpha was not so impressive as a full disk, so I did a crop of just the right hand side, then rotated and inverted. This image is a stack of 8 frames. If you click on the image, you can see it at high resolution. The fine details are not that distinct, probably because of unfavourable seeing. Since it takes quite a bit of time to scan the full disk (around 10 sec), the SHG method requires very stable atmospheric conditions.

H-alpha SHG image, 106mm aperture, f6.8. 2400 l/mm grating, stack of 8.
H-alpha SHG image, 106mm aperture, f6.8. 2400 l/mm grating, stack of 8.
290722-Ha-720mm-stack-8-20_invert.jpg (634.93 KiB) Viewed 1148 times

This was the first real imaging run with our new SHG equipment setup. There is a small optical alignment problem with the camera lens, which may explain why the left side of the images are not as sharp as the right. Correcting this alignment issue may require a bit of machining but we plan to fix it in the near future. We are hoping to eventually be in good focus across the whole solar disk.

Edit: after making some modifications, I came to the conclusion that the remaining optical issue was likely just a slight tilt of the plane of the slit. I added a TS tilt corrector in front of the slit. The amount of correction was very small, maybe equivalent to about 20 microns across the full length of the 12mm long slit. But that's probably enough to account for the residual focus issues I was noticing. That amount of tilt is not surprising considering the number of extension tubes, etc, attached to the focuser of the telescope.
Last edited by thesmiths on Sat Jul 30, 2022 3:42 pm, edited 4 times in total.


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by marktownley »

Very nice Douglas!

Have you a 16 bit version of the CaK disk you could share - stacked but no sharpening etc? Would like to have a play with it :)


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by thesmiths »

marktownley wrote: Sat Jul 30, 2022 2:36 pm Have you a 16 bit version of the CaK disk you could share -- stacked but no sharpening etc?
Yes, I can send you the CaH output from AS3! to you. It's 24.5MB. Let me know what's the best way. There are lots of details in there, including prominences. The sky background is not entirely dark, however (common issue with the method).

If you really want to play around, you can even restack yourself. There were 15 good frames, 225 MB. They were all quite high quality so I chose to stack the "best" 13 (according to AS's criteria). I started off with 20 frames (which corresponds to scanning back and forth 10 times) and eliminated 5 manually. The original 20 scans is 75.2 GB of data. It's a disk drive intensive business.


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by fulvio.mete »

Excellent spectroheliograms, Douglas , congratulations


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by marktownley »

thesmiths wrote: Sat Jul 30, 2022 3:20 pm
marktownley wrote: Sat Jul 30, 2022 2:36 pm Have you a 16 bit version of the CaK disk you could share -- stacked but no sharpening etc?
Yes, I can send you the CaH output from AS3! to you. It's 24.5MB. Let me know what's the best way. There are lots of details in there, including prominences. The sky background is not entirely dark, however (common issue with the method).

If you really want to play around, you can even restack yourself. There were 15 good frames, 225 MB. They were all quite high quality so I chose to stack the "best" 13 (according to AS's criteria). I started off with 20 frames (which corresponds to scanning back and forth 10 times) and eliminated 5 manually. The original 20 scans is 75.2 GB of data. It's a disk drive intensive business.
Just attach the 24.5Mb file to a post, can download it that way. Thanks!


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by marktownley »

Heya Doglas,

I'm not sure I came up with anything much different than you. Interesting to play with new data like this. Be very interested to process a CaK one at some point and see what it looks like.
Douglas-CaK.jpg
Douglas-CaK.jpg (2.99 MiB) Viewed 1054 times
Mark


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Re: CaH and H-beta full-disk SHG images -- good resolution, July 29

Post by DeepSolar64 »

All three of these look really nice but I notice the Hb image the most. What level of the chromosphere does H-beta see? CaH and CaK see the lower levels of the chromosphere right above the transition level to the photosphere. Ha shows higher up. My guess is that Hb shows a layer in between Ha and CaK. It certainly shows the chromospheric network mottles well.

Two thumbs up! SHGs are awesome!!


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