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Hubble palette tutoriel
It would be really fantastic to have a complete tutorial to know the image processing technique to make a Ha-SII-OIII image 😀
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...
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:
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.
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:
What targets have you been trying to image? What exposures have you tried?
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
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.)
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?"
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
Thanks @Kijja I need to try mixing NB and RGB.
This blog post by SWAG was helpful:
Also she linked to this article:
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.