Stacking Spectra with Sharpcap!

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James Ley
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Joined: Sun Apr 14, 2019 7:42 pm

Stacking Spectra with Sharpcap!

Post by James Ley » Sun Apr 14, 2019 8:58 pm

I'm sure this is something that the creative genius behind Sharpcap never thought of, but there's no harm in asking.

By passing starlight through a grating, one can generate an image of both the star and its spectrum.
https://www.shelyak.com/produit/star-analyser/?lang=en
I have been acquiring such images using Sharpcap (excellent software, thank you very much). Here is a slightly unusual example of Mizar AB and Alcor (often there is only one star in the image). You can see the star to the left and the line, which is the spectrum, to the right.
Mizar AB and Alcor annotated.jpg
Mizar AB and Alcor annotated.jpg (17.13 KiB) Viewed 80 times
What would take this to the next level is to be able to stack several spectra. Unfortunately, there are often not enough stars. If I just stack without any alignment, then the spectral features get blurred and lost (due to poor tracking).There are three obvious points that Sharpcap could use to align the images, if i could enter them manually: the star, some point on the left of the spectrum and some point on the right. Then maybe Sharpcap could use it's regular algorithm to align and stack the images based on these three points.

Does anyone have any ideas on how I might stack such images? Thanks.

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admin
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Re: Stacking Spectra with Sharpcap!

Post by admin » Mon Apr 15, 2019 4:55 pm

Hi,

Does SharpCap managed to detect any of the stars you try to attempt stacking on those images? There is a checkbox in the alignment settings that you can use to make SharpCap highlight the stars that is detected. (I'm assuming here that the image that you get on the sensor is like the one you shared – i.e. part of it is a normal image of the stars and part is a spectrogram).

Cheers, Robin

James Ley
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Joined: Sun Apr 14, 2019 7:42 pm

Re: Stacking Spectra with Sharpcap!

Post by James Ley » Fri Apr 19, 2019 1:41 am

Thanks for your Reply Robin and congratulations on your wonderful software.

Unfortunately no, many of my images/spectra only have one star. There isn’t any rotation in the image. The star and spectrum move (are translated) mostly due to poor tracking. To focus the spectrum the star image is slightly defocused so hopefully it’s not bigger than Sharpcap can handle. But I don’t see how to stack on only one point.
Cheers,
Jim

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Re: Stacking Spectra with Sharpcap!

Post by admin » Fri Apr 19, 2019 7:56 pm

Hi Jim,

Actually, that was pretty much what I needed to know – the fact that there is a single star means that in theory it would be possible for me to update the code to track a single star in the XY directions without worrying about field rotation. This could either be done by detecting a single star in the frame or working on something simpler like the 'centre of mass' of the brightness of the frame.

I will consider this as a feature for a future version.

Cheers, Robin

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