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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 14:02  

Hello,

It would be really fantastic to have a complete tutorial to know the image processing technique to make a Ha-SII-OIII image 😀 

Thanks,

Patrick

This topic was modified 5 months ago by Vincent Groenewold - Moderator

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 3, 2019 19:55  

Up Voted +100

So far I've had success with Bi-Color, specifically HOO. A great unknown to me is if I should capture twice the number of OIII frames because I'm splitting the signal between green and blue?

Patrick, thanks for raising this topic!


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 20:04  

Hello oopfan,

I did the experiment for the combination of the SHO and it was not a success with APP and my image was only green it is certain that I haved not the good technique. I'm going to wait for Mabula to make a suberb tutorial as he usually does before, I get back to the project. The Ha-OIII result is impressive too ...

To be continued...

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 3, 2019 20:22  

Hi Patrick,

I agree. With Hubble Palette, hydrogen alpha is assigned green. Many narrowband objects we image are predominantly hydrogen with "trace" amounts of oxygen and sulfur. By "trace" amounts I mean that the signal is much weaker than Ha.

What I've discovered is that with my Atik 314E CCD with 5e- Read Noise I can capture Ha very well with an 8-minute exposure but OIII and SII require at least a 15-minute exposure. On Sara Wager's website you can see that she regularly uses 30-minute exposures for each filter. In my experience 30 minutes will capture good signal-to-noise on a single frame in all filters. That's the key to making a good narrowband image. BTW. my scope is f/5.9 so if your scope is faster then you can you shorter exposures.

I am in the early stages of experimentation now but here are two HOO images I made of a section of the Soul Nebula. The bloody red one is strictly HOO: 100% Ha->Red, 50% OIII -> Green, 50% OIII -> Blue. The other one more closely matches Sara's image. With it I am feeding the Green channel with a little bit of Ha.

Here is Sara's image:

https://www.swagastro.com/ic1871.html

Soul Rift HOO Ha 20x480s OIII10x900s rev2
Soul Rift HOO Ha 20x480s OIII10x900s Ha R80 G20 OIII G30 B70


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 21:43  

Hi oopfan,

Good, thanks  for sharing..  if you have develloping some technics of avancement keep me inform  😉 

Best regards,

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 3, 2019 22:07  

Hi Patrick,

I will do that. I'll begin by shedding some light on "Integration Time". Many people think that a stack of 100 1-second exposures is equivalent to 1 100-second exposure. It is true if you want to know how much time you spent at the telescope but in terms of signal-to-noise it is not equivalent.

Signal-to-noise (SNR) is proportional to: (Exposure1 / Exposure0) * SQRT (Frames1 / Frames0)

In other words if you double the exposure but keep the frame count the same then you double the SNR, however if you double the frame count but keep the exposure the same then you increase SNR by only 41%. This is why I always advocate increasing exposure whenever possible. Some people can't because of light pollution or guiding problems.

Manipulating exposure is the single greatest lever you can pull to improve your images. Frame count is a distant second place.

 


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 22:14  

Hi Oopfan,

Yes i agree, that is the method i use for better signal noise ratio i haved a Paramount MX+ and my observatory are located in a dark sky location(backyard observatory) its not a problem for me to take long exposures.

Patrick

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 3, 2019 22:16  

Great! What is the f/ratio of your scope? What is the bandwidth of your NB filters?


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 22:24  

I haved two Takahashi  one FSQ-85 F/5.3 and reducer F/3.8 and  one TOA-130FNB F/7.7  2 x STF-8300m whit Astrodons filters GEN-2 Ha 5nm and LRGB

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 3, 2019 23:08  

Patrick,

The STF-8300m has a pixel size of 5.4um.

Using the FSQ-85 with reducer at f/3.8 the focal length is 323mm therefore resolution is 3.45 arcsec/pixel. Unfortunately you are seriously under-sampling.

Using the FSQ-85 without the reducer at f/5.3 the focal length is 451mm therefore resolution is 2.47 arcsec/pixel. You are still under-sampling but not as severely.

Short focal length scopes really need a small pixel size camera. With the reducer I recommend a pixel size of 2um. Without the reducer you can get by with 3um. I think that ZWO makes CMOS cameras having 2.1um.

Using the TOA-130FNB at f/7.7 the focal length is 1000mm therefore resolution is 1.11 arcsec/pixel. Your camera is perfectly suited for this telescope!

This is what I suggest you do:

1. Use bin2 mode in order to shorten total integration time. (This is the technique that Sara Wager and I use.) Remember that you can always drizzle after you've captured enough data.

2. Use 30-minute exposures for each of your NB filters.

3. Research your targets before committing time. I use Sara Wager's website for inspiration. There is another website that I'll list below:

https://www.swagastro.com/images-gallery.html

http://sharplesscatalog.com/narrowband.aspx

https://astronomy.tools/calculators/ccd_suitability

What targets have you been trying to image? What exposures have you tried?

 


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 3, 2019 23:27  

Yes indeed, I give you reason, on the other hand it is not always obvious to have a perfect combo to respect an ideal sampling and for a questions of budjet.

There is also my region in Quebec that never goes down by 1.75 "/ pixels when it comes to the quality of the sky and we have maximum 60 nights per year so I can not do longer projects.
For the TOA I just received it and my objectives is to realize my subs exposures in 900secs for the LRGB and 1200secs for the NB 

Here is the address of my website you can see my images and installation

https://www.patrickdubeastroimaging.com/LRGB-Gallery/

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 4, 2019 00:16  

OK, I see your point about seeing conditions. I didn't have that information for my analysis.

So you just have the Ha filter? No other narrowband filters? APP has video tutorials on LHaRGB.

(My friend lives outside Toronto. He complains about the weather constantly. He is thinking about selling his kit and replacing it with goldfish 😀  My weather outside New York City isn't much better. I am lucky if I get four nights per month.)

 


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(@patrick)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 39
November 4, 2019 01:37  

Yes i haved only Ha filter for the moments but i use the SHO pallete acquisition of my friend to practice SHO worflow in APP but its not good for the moment  😉 

Patrick Dubé


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 4, 2019 04:26  

Patrick,

Perhaps you should start a new topic and say:

"My friend lent me his narrowband data of "X" to see if I could replicate his results using APP. He used "Y" and "Z" to process it. It came out nice (see attachment). When I try to do it in APP I get one color: Green (see attachment). Can someone help me figure out what I'm doing wrong?"


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(@kijja)
Neutron Star Customer
Joined: 2 years ago
Posts: 101
November 5, 2019 02:48  

@oopfan
I found that if I change HOORGB to  HHORGB ( assign Ha to red and green Oiii to blue and keep mono R GB as their own channels)  will create image similar to SHO palette. Don’t know if this will work on duo-narrow band or not  

HHO RGB

4273CB41 A00F 4636 8E1F 42614791E471

 

 
This post was modified 5 months ago by Kijja

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(@kijja)
Neutron Star Customer
Joined: 2 years ago
Posts: 101
November 5, 2019 03:14  

one thing I might forgot, after rgb combine SHO images are very green  We need to calibrate background and star color calibration and selective color adjustments as well  

Kijja 


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(@oopfan)
Red Giant Customer
Joined: 1 year ago
Posts: 85
November 5, 2019 21:01  

Thanks @Kijja I need to try mixing NB and RGB.

This blog post by SWAG was helpful:

https://www.swagastro.com/start--finish---processing-is-the-key.html

Also she linked to this article:

http://bf-astro.com/hubblep.htm

This opened my eyes to what I've been doing wrong. They advocate stretching the stacks before combining. I was doing it in reverse: combining then stretching. So in order to "tame" the Ha stack I aggressively stretch the SII and OIII. Also, I assign 50% of Ha to Green and 50% to Luminance.

In the attached image of the PacMan nebula I captured a mere 3 hours so keep that in mind when judging the quality. It really needs 10 hours or more. Also, I captured in bin2 mode to boost the signal and then used APP to drizzle 2x. These are 8-minute exposures using 6nm SII, Ha, and OIII. Atik 314E. William Optics 71mm f/5.9.

PacMan SHO rev1


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