H-alpha and CaK full-disk SHG images -- plus CaK proms

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thesmiths
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H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by thesmiths »

The sky over London was clear and the air was quite still today so even better results were obtained in the most recent testing of the long chrome/quartz slits (for the previous test run see viewtopic.php?t=36602). I used the setup from the day before to take four H-alpha scans and then tuned the grating to the H/K lines of Calcium. The focus points for all three optics needed to be adjusted slightly at the shorter wavelength but this did not take too much time. The results at CaK looked a little nicer than the ones at CaH so I present CaK and H-alpha.

Since I was using no attenuation (e.g. ND filter) of the solar energy, the shutter speed could be kept at 1ms for both H-alpha and CaK. The gain for H-alpha was 9% and for CaK it was 30%. Both ROI had a length of 3200, with the H-alpha width 180 and for CaK 200 (the greater width was needed because the CaK line is significantly wider than H-alpha). The H-alpha scan rate was 12x sidereal rate and 10x for CaK (since the FPS was 257 and 231).

For the H-alpha processing I again used Valerie Desnoux's software Solex_ser_recon v3.3.0, while for CaK, I used our own Solex_ser_recon_EN version 3.2 (https://github.com/thelondonsmiths/Sole ... s/tag/v3.2). Hers gives much fewer line errors with H-alpha, while ours works better on Calcium images.

H-alpha SHG image, 9 micron x 12 mm chrome/quartz slit, 2400 l/mm holographic grating, 183MM camera. 106mm x 700mm APO triplet refractor at full aperture. June 15, 11:15 UTC.
H-alpha SHG image, 9 micron x 12 mm chrome/quartz slit, 2400 l/mm holographic grating, 183MM camera. 106mm x 700mm APO triplet refractor at full aperture. June 15, 11:15 UTC.
111512_clahe.jpg (380.62 KiB) Viewed 874 times
CaK SHG image (a slight rotation of the camera was made after the H-alpha imaging). June 15, 12:42 UTC.
CaK SHG image (a slight rotation of the camera was made after the H-alpha imaging). June 15, 12:42 UTC.
124201_clahe.jpg (385.17 KiB) Viewed 874 times
CaK prominence image
CaK prominence image
124121_protus.jpg (68.08 KiB) Viewed 874 times
Last edited by thesmiths on Thu Jun 16, 2022 5:59 pm, edited 2 times in total.


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by Montana »

These are just absolutely incredible, some of the best SHG images I have ever seen :bow :bow :bow

Alexandra


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by thesmiths »

I will add here a reduced size side-by-side comparison, which enables matching the small features more easily, in particular the filaments. I think filaments only appear clearly with quite narrowband imaging.

H-alpha vs CaK, SHG at 700mm by 106mm, June 15
H-alpha vs CaK, SHG at 700mm by 106mm, June 15
111512_124201_small.jpg (106.28 KiB) Viewed 831 times

There was a small camera rotation done between the two images so the two cannot be overlayed without a derotation. I should mention that the original data was taken at 3200 pixel width and the large images above were reduced by 50% to 1600 pixels. The small ones here were reduced to 500 pixels.


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by marktownley »

Impressive!


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by p_zetner »

These are very good!
I certainly agree that, apart from H alpha, "filaments only appear clearly with quite narrowband imaging".
Your results are making wonder if I should give the "fast scan" technique a try!
Cheers.
Peter


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by thesmiths »

p_zetner wrote: Fri Jun 17, 2022 2:38 am Your results are making wonder if I should give the "fast scan" technique a try!
Fast scanning is definitely the way to go. You get a much higher probability of success (but a lot more disk space used).


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by fulvio.mete »

Hi, Douglas, very nice images!
It seems your quarz/chrome slits works well.What about the camera you used?
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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by thesmiths »

fulvio.mete wrote: Fri Jun 17, 2022 4:02 pm What about the camera you used?
Fulvio
I was using the ZWO 178MM but I recently decided to "upgrade" to a ZWO 183MM. The sensor is essentially the same, as far as I can tell; it is just larger (and the dimensions of the case is slightly different too, which changes the focal point). The extra size is helpful for the large slit length but it is not essential (the ZWO 178MM is quite a bit cheaper, $300 vs $700). Assuming a 1:1 projection of the slit on the camera sensor, the 178MM (with a width of 7.4mm) is big enough for 700mm focal length but not big enough for 800mm.

I should note that I tried a focal length of 910mm and there was the problem that the illumination dropped off a lot along one of the edges. I think with the small optics I am using (25mm diameter) there needs to be really good alignment of the optics or there will be very visible "vignetting". Like when using larger format film, bigger optics is required for taking pictures (and also printing -- what the collimator does is more analogous to an an enlarger lens). I should also mention that "smile" increases with slit length, which causes its own problems (and I have always had difficulty minimising this effect).


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by Carbon60 »

These are incredible SHG images. Nice work.

Stu.


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Re: H-alpha and CaK full-disk SHG images -- plus CaK proms

Post by ChrisHalpha2017 »

Very nice!!! I really should give it a try !! Your images are inspiring !!


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