Comparison between G band and K-line filters

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christian viladrich
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Comparison between G band and K-line filters

Post by christian viladrich » Wed Dec 27, 2017 10:33 am

Dear All,

Here is a comparison between a G band filter (430 nm FWHM 2 nm) and a K-line filter (396 nm FWHM 10 nm). The seeing conditions were about the same for both images. The processing is exactly the same.

On the overall, the K-line and the G band images look about the same. The contrasts of the solar granulation and of the facular regions are similar.

The main difference is the slightly lower resolution of the K-line image due to the shorter wavelength (seeing gets worse with shorter wavelength).

Image

Image

With the 150 mm aperture, the result with a 430 nm FWHM 10nm is similar to the result with the 430 nm FWHM 2 nm. This is not the case with larger apertures. The smaller FWHM increases the contrast of intergranular bright spots.

In optimal seeing conditions, the K-line filter takes the lead thanks to the slighly larger resolution due to shorter wavelength (= reduced diffraction).

All in all, this makes the G-band filter an interesting alternative to the K-line filter.

Best regards
Christian Viladrich
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Re: Comparison between G band and K-line filters

Post by dvoss » Wed Dec 27, 2017 2:54 pm

Great images, Christian. I take it that the G-band is picking up both calcium and iron lines, or is it just calcium in the 2nm bandpass?

David

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Re: Comparison between G band and K-line filters

Post by Valery » Wed Dec 27, 2017 4:40 pm

Well done, Christian! Very illustrative for imagers.

Have you inaged this group in a Ca II K line?


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Re: Comparison between G band and K-line filters

Post by Valery » Wed Dec 27, 2017 4:41 pm

And, one question, Christian, if I may.

How do you process the images that near limb ares are same clean and detailed as the ares far from the limb.

I believe we all have the largest problems processing the near limb areas.


Thanks,

Valery
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Re: Comparison between G band and K-line filters

Post by Montana » Wed Dec 27, 2017 5:57 pm

These are great :bow :bow
I agree with Valery, how do you get your limb shots so good :)
Is that a Baader K line filter? or a Lunt CaK filter?
Alexandra


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Re: Comparison between G band and K-line filters

Post by MapleRidge » Wed Dec 27, 2017 11:29 pm

Superb comparison Christian :bow

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Re: Comparison between G band and K-line filters

Post by Merlin66 » Thu Dec 28, 2017 6:04 am

Good, well processed images ....
There's no calcium around 430nm....
I do think the K line filter brings out a bit more detail in the outlying plage areas
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Re: Comparison between G band and K-line filters

Post by marktownley » Thu Dec 28, 2017 8:40 am

Good comparison thanks!
Image
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Re: Comparison between G band and K-line filters

Post by christian viladrich » Thu Dec 28, 2017 10:54 am

Thanks to all !
David : the G band is one of the lines named by Fraunhaufer. It is a group of CH lines with a FWHM of about 1 nm. The Ca II lines are farther to the near UV.
Valery : I did not taken any Ca K image of this group. In fact, I was comparing the Baader K-line, the Edmund Optic 430 nm FWHM 10nm, and the Andover 430 nm FWHM 2 nm.
BTW, the images were very pleasing visually with the G band filter, with a nice blue color and a lot of contrast in the granulation. The continuum gave less contrast. as for the K-line, It was far too blue for me.
As for the processing, there is nothing special. I just apply an unsharp mask filter over the whole image (k= 8, sigma = 1.4 pixel).
Alexandra : yes, this is the Baader K-line filter.
Ken : yes, there is a bit of more detail and contrast in the plage area with the K line. BTW, I really enjoyed your book. It is very well done !
Christian Viladrich
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Re: Comparison between G band and K-line filters

Post by yltansg » Thu Dec 28, 2017 2:23 pm

Hi Christian,

Thanks for sharing your findings. An eye opener for me.

Alfred

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