Extract SII channel...
 
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Extract SII channel from OSC image  

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(@stuartt)
Brown Dwarf Customer
Joined: 6 months ago
Posts: 8
October 8, 2021 12:14  

I shoot with an OSC and I want to create Hubble palette images. 

I understand that I first need to extract the OIII, Ha and SII channels from my colour image and then re-combine them.

I can extract Ha and OIII in APP, but there seems to be no option to extract SII. Is this correct? If so, when you you plan to add that? It seems odd to leave one of the channels out.

Thanks


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3961
October 8, 2021 12:18  

SII will be mixed into the spectrum of the Ha and OIII if you used a dualband-filter. If you specifically want SII, you need a filter for that. Software can't distinguish specific wavelengths. And when you have the SII data, you can select SII in the algorithm. The extract options are meant for dualband filters.


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(@stuartt)
Brown Dwarf Customer
Joined: 6 months ago
Posts: 8
October 8, 2021 12:27  

Thanks Vincent. Sorry I am new to all this!

If software cannot distinguish different wavelengths, then how can it do this for Ha and OIII from a colour image? 

I am using a optolong L-extreme filter. Does this mean I can only extract Ha and OIII in APP?

If so, how can I make a Hubble palette image?

Thank you 🙂

This post was modified 2 months ago by Stuart Taylor

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(@vincent-mod)
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Joined: 4 years ago
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October 8, 2021 13:55  

No problem, this is quite a tricky thing sometimes. For a dual channel filter, most of the Ha will be captured in the red channel and OIII in the green/blue channel. APP can nicely and with retaining the original resolution, separate those channels automatically. But that's all it can do, the signal lands on your sensor and is filtered by the bayer-matrix to red, green and blue. This is all APP can see and it can't distinguish between signals within that. To be able to really get the signals you want, you need filters that you know will only let through e.g. SII. The L-extreme is a dual-band filter and indeed can only separate Ha and OIII, for SII you'd need a SII filter. Ideally, a mono sensor with filters for OIII, Ha and SII are used.


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(@stuartt)
Brown Dwarf Customer
Joined: 6 months ago
Posts: 8
October 8, 2021 14:15  
Posted by: @vincent-mod

No problem, this is quite a tricky thing sometimes. For a dual channel filter, most of the Ha will be captured in the red channel and OIII in the green/blue channel. APP can nicely and with retaining the original resolution, separate those channels automatically. But that's all it can do, the signal lands on your sensor and is filtered by the bayer-matrix to red, green and blue. This is all APP can see and it can't distinguish between signals within that. To be able to really get the signals you want, you need filters that you know will only let through e.g. SII. The L-extreme is a dual-band filter and indeed can only separate Ha and OIII, for SII you'd need a SII filter. Ideally, a mono sensor with filters for OIII, Ha and SII are used.

Ah, yes. Of course. APP can separate OIII and Ha because they mostly fall in B and R pixels. But because the SII emission is also red it gets mixed with the Ha and so APP has no way to separate it. This makes sense.

So I am thinking that if I shoot with OSC and l-extreme then use APP to generate the OIII and Ha channels, I then shoot again using a SII filter. Then I have all three channels and can combine them to make a Hubble palette image.

I guess the only problem is that SII is weak and the Bayer matrix will reduce this still further. So I would need a LOT of subs!


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(@vincent-mod)
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Joined: 4 years ago
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October 8, 2021 14:19  

Long exposures mainly, more so than many subs in the case of narrowband. The more the better, but per sub you also want as much signal as possible. 15 min exposures are actually used quite often. This is where mono sensors indeed can have an advantage, as the entire sensor can be used to collect signal. Though modern color sensors are quite good as well.


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