RCC - ways to improve acquisition and processing, 1 year into astrophotography Requests for constructive critique · AstroÅmazer · ... · 15 · 408 · 0

AstroÅmazer 0.00
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Monday, June 16th was exactly 1 year since my first astrophotography session with a 85mm lens on an astro-modified Nikon Z5 MILC and a SW SA GTi mount. Since then, I have tried various camera lenses and 3 smallish refractors. My current rig is a WO GT81 IV + Flat GT with a ZWO ASI585MC Pro on a ZWO AM3. I use a ZWO ASIAir Mini for capture/control. Here is my latest astrophotograph with this rig:
Ha+RGB+IR:
https://app.astrobin.com/u/Astro%C3%85mazer?i=i8ask6#gallery
RGB+IR:
https://app.astrobin.com/u/Astro%C3%85mazer?i=i8ask6&r=B

This is going to be a very detailed post so thanks in advance for reading till the end!

Acquisition wise, here is my most recent process:
1. Try to plan Luminance around 3rd quarter to 1st quarter and Narrow Band around the rest of the month.
2. Try to stay at least 75 degrees away from the moon even when using NB filters
3. If seeing is bad, or have to get Luminance data between 1st quarter and 3rd quarter of the moon, use the IR Pass filter
4. Get at least 16 darks, 32 flats, 16 dark flats (Re-thinking this, may not need darks) 
5. If initial polar alignment is off by more than 2 degrees, repeat after 1st try
6. If changes to RA affects Dec while polar alignment, mount isn't perfectly level, bump up guiding aggression a little
7. Re-run guiding calibration if rig was disassembled/moved
8. Acclimatize scope ~30mins-1hr before session
9. Autofocus every 2hrs/2 degrees C change in ambient temperature
10. Dither, dither, dither - though lost ~40 pixels each side on this project before field rotation issues between nights.
10. Gain 252, 30s subs for stars, 60s for Lum, 90s for IR Pass, 180s for NB 
11. There is some tilt in my imaging train which I am trying to fix!!!

I am using a WO 120mm guide scope with a ASI220MM Mini and getting ~0.6" guiding accuracy. Mean FWHM has been between 3"-4" recently. On a bad night like June 3rd, the sky looks very orange (smoke from Canadian wildfires?). On a good night like June 4th, I can see Andromeda rising with my 10x42mm binoculars. Have had less than 10 clear nights all spring. 

Processing wise, I use Siril/Gimp/GraXpert/StarNet++. Here is what I have been doing:
1. I use a modified version of the OSC preprocessing script with drizzle, in Siril. Modifications:
    a. Use weighted FWHM as a metric for stacking.
    b. When stacking Ha, stack on red channel.
2. Stack data from each night separately.
    a. I can write a script to customize this so that all calibration is done with flats etc per night and registration/stacking is done with all subs at once.
    b. Do not have hard disk space to do all at once registration/stacking sometimes so do my own weighted stacking of different batches.
3. I keep the registration FWHM and background CSVs and use them to weigh each night's stack.
4. Once I have the stacks for each filter, I do the following in linear:
    a. Desaturate stars if needed (does this make my data non-linear?)
    b. Run the AberrationRemover.py script.
    c. GraXpert background extraction.
    d. Plate solve.
    e. Color calibration - Spectrophotometric if filter analogue is available else Photometric.
5. At this point I remove the stars. For the stars, I use the Modified ArchSinH Transform. Stretch to my liking, add some saturation etc.
6. As for stretching the starless image, I process each filter separately and blend in the stretched data. Try to keep the sky brightness peak < 0.1 and bring out the features I am after.
7. I mostly use the StatisticalStretch.py script, GHS and some Curves, maybe some CLAHE at the end.
    a. In GHS, I use Independent Channel Values or Saturation for the stretch model and RGB blend for the clip mode.
    b. Have noticed other combinations can lead to values > 1
8. Then I go over to Gimp, reduce the color noise in the background with the Hue-Chroma tool.  Add some cosmetic healing if the stars were not removed well enough or have issues with flats.
    a. I have tried decomposing to Lab space and sharpening L, blurring a and b to some level of success but mostly reducing chroma and lightness a little in the Hue-Chroma tool is good enough.
9. After blending in the broadband data to my liking (In this example, I weighed the Lum and IR data by FWHM and background level) I get Continuum Subtracted NB using the Siril script and use Pixel Math to compose my final image.
10. If I am doing a SHO processing, I try Dynamic NB equations or custom static blends based on the IMX585 sensor's response to the NB wavelengths.
11. Finally, blend in the stars using Pixel Math. Apply subtle GHS/curves/saturation adjustments if required.
12. Run GraXpert denoise till the grain is smoothened out. I feel like I am denoising too much. But if I don't, I end up with a lot of speckle/grain.

Again, thanks if you stuck around till here. And thanks in advance for any feedback!!!

CS
GD
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afd33 9.38
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For 4 in the acquisition section. You have a cooled camera; there's no reason not to use dark frames. On a night when you're not imaging make a dark library of common exposure times that you shoot. I do 30, 60, 90, 120, 300, and 500 seconds. 20 of each. Stack them, and now you have master darks that you can use for at least a year generally. Then since the newer cameras with no amp glow I don't use dark flats, but I do use bias frames. My flats seem to correct well so it works for me.


I'm not familiar with Siril, but what's the point of de-saturating the stars?
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AstroÅmazer 0.00
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Quinn Groessl:
For 4 in the acquisition section. You have a cooled camera; there's no reason not to use dark frames. On a night when you're not imaging make a dark library of common exposure times that you shoot. I do 30, 60, 90, 120, 300, and 500 seconds. 20 of each. Stack them, and now you have master darks that you can use for at least a year generally. Then since the newer cameras with no amp glow I don't use dark flats, but I do use bias frames. My flats seem to correct well so it works for me.


I'm not familiar with Siril, but what's the point of de-saturating the stars?

Helps if stars are clipped, which given 585's HCG of 252, happens frequently. Uses a Moffat profile approximation to fix clipped stars.
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bigCatAstro 0.00
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Nice process!  I’m too lazy to desaturate stars, so kudos to you.
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andreatax 9.89
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AstroÅmazer:
1. Try to plan Luminance around 3rd quarter to 1st quarter and Narrow Band around the rest of the month.
2. Try to stay at least 75 degrees away from the moon even when using NB filters
3. If seeing is bad, or have to get Luminance data between 1st quarter and 3rd quarter of the moon, use the IR Pass filter
4. Get at least 16 darks, 32 flats, 16 dark flats (Re-thinking this, may not need darks) 
5. If initial polar alignment is off by more than 2 degrees, repeat after 1st try
6. If changes to RA affects Dec while polar alignment, mount isn't perfectly level, bump up guiding aggression a little
7. Re-run guiding calibration if rig was disassembled/moved
8. Acclimatize scope ~30mins-1hr before session
9. Autofocus every 2hrs/2 degrees C change in ambient temperature
10. Dither, dither, dither - though lost ~40 pixels each side on this project before field rotation issues between nights.
10. Gain 252, 30s subs for stars, 60s for Lum, 90s for IR Pass, 180s for NB 
11. There is some tilt in my imaging train which I am trying to fix!!!


1. That depends but in general I'd agree in principle. In practice it depends on how far the Moon is and what's its altitude. 
2. That depends on the NB filters you have. If they are tight then you can get much closer. Also depends on the Moon phase.
3. Don't.
4. See other recommendations about building a dark library and you don't need as many flats.
5. You should never be in that position. Get SharpCap Pro and be done with it.
6. Not quite clear what you mean by this but in general unless you're heavily tilted PA doesn't depend on the mount being flat.
7. In general, yes, you'd want to do that.
8. That depends on the scope but yes, is good to wait for the scope to cool off a bit.
9. Depends on the scope and how fast it is, some of mine never need beyond initial focus. YMMV.
10. I never dither. Dither is a waste of time. You are into imaging not getting your statistics tip-top.
11. That's up to you. 
12. Getting tilt fixed should be a high priority item on the agenda.
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messierman3000 7.22
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andrea tasselli:
10. Dither is a waste of time.


I thought it reduces walking noise?
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dahackne 1.51
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My quick comments that you're welcome to disregard:
  • As others have mentioned, create a dark library so you don't need to waste time in the field on darks. Though your exposure times are incredibly long, taking 16 darks at 120 second exposure times is over half an hour of time you could be collecting lights. I take darks every 8-12 months to capture any changes to my sensor (i.e. a pixel dies).
  • Pick sensor temperatures to always shoot at that match your dark library. I have dark libraries at 0°C and 20°C for warm, humid nights where my camera can't cool the sensor to 0°C.
  • For your exposure times, I think biases will work just as well as dark flats. They're easier to take with the ASIAir software, and a little faster.
  • Buy a bubble level to make sure the tripod/mount are level as you're setting up. If you're using the carbon fiber tripod that you can buy with the AM3, I'd make sure the tripod is level before putting the mount on the tripod.
  • How are you polar aligning? I use an ASIAir and I have an AM3, and using the ASIAir app's polar alignment routine should get your polar alignment much better than 2°.
  • This may be unpopular, but at your focal length (478 mm), I wouldn't worry about seeing too much.
  • I autofocus every hour, but that could be personal preference.
  • There was a discussion on another topic about flats from imagers much more experienced than me: if you rotate your to frame objects how you want, make sure to take your flats at the same rotation as you're taking lights. Dust motes won't properly calibrate out otherwise.
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andreatax 9.89
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Oscar:
I thought it reduces walking noise?


*Maybe with old DSLRs but with modern cooled sensors you shan't have any if you have the proper processing pipeline in place.
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AstroÅmazer 0.00
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andrea tasselli:
Oscar:
I thought it reduces walking noise?


*Maybe with old DSLRs but with modern cooled sensors you shan't have any if you have the proper processing pipeline in place.

I haven't tried no dithering with my 585/AM3 rig but I dither every 120s/180s so 4-6 30s exposures. Will try no dither and see how it goes.

The Z5/SW SA GTi setup I use definitely has lots of walking noise. But it is useless trying to dither on the GTi.
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Aripaule 1.20
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hi,



I think Pixinsight with RC astro plugins would make a good difference in your results,


I also think you should make more RGB frames, so more "natural" colors of the object stand out, since your Bortle is very good.

And a question: Why IR pass? What is your idea with it?
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AstroÅmazer 0.00
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Drew Hackney:
My quick comments that you're welcome to disregard:
  • As others have mentioned, create a dark library so you don't need to waste time in the field on darks. Though your exposure times are incredibly long, taking 16 darks at 120 second exposure times is over half an hour of time you could be collecting lights. I take darks every 8-12 months to capture any changes to my sensor (i.e. a pixel dies).
  • Pick sensor temperatures to always shoot at that match your dark library. I have dark libraries at 0°C and 20°C for warm, humid nights where my camera can't cool the sensor to 0°C.
  • For your exposure times, I think biases will work just as well as dark flats. They're easier to take with the ASIAir software, and a little faster.
  • Buy a bubble level to make sure the tripod/mount are level as you're setting up. If you're using the carbon fiber tripod that you can buy with the AM3, I'd make sure the tripod is level before putting the mount on the tripod.
  • How are you polar aligning? I use an ASIAir and I have an AM3, and using the ASIAir app's polar alignment routine should get your polar alignment much better than 2°.
  • This may be unpopular, but at your focal length (478 mm), I wouldn't worry about seeing too much.
  • I autofocus every hour, but that could be personal preference.
  • There was a discussion on another topic about flats from imagers much more experienced than me: if you rotate your to frame objects how you want, make sure to take your flats at the same rotation as you're taking lights. Dust motes won't properly calibrate out otherwise.

I take flats every session so no rotation in between. They are fast. So no worries there.

Darks, I have a library for -20°C. Rest am building as I shoot. Have had the camera for 6 months so need to figure out my summer temp and a temp range in between. I collect darks before or after sessions, either when the scope is acclimatizing or before stowing it.

My PA is generally under 1'. I meant if the starting estimate is > 2°, I finish PA and redo it. PA accuracy depends on initial estimate. Even if ASIAir reports under 1', it is relative to the initial estimate. Slewing and rechecking PA always shows a different value if the initial estimate was > 2° off.

I have given up trying to level the tripod. I shoot on grass, so even when the tripod is level without the mount on it, it seems to shift after. Playing with aggression on ASIAir takes care of it. I tune aggression till my dither settling time is under 5s. Then am set for the night.

At 478mm with 2.9um pixels, I am definitely seeing limited. My pixel scale is ~1.25"/px but seeing has been 3"/px or worse all spring as measured by Siril in the FWHM plot.
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AstroÅmazer 0.00
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Ari Paulechen Junior:
hi,



I think Pixinsight with RC astro plugins would make a good difference in your results,


I also think you should make more RGB frames, so more "natural" colors of the object stand out, since your Bortle is very good.

And a question: Why IR pass? What is your idea with it?

I am holding off on Pixinsight till I have a better handle on things and a better rig.

My Bortle 5 skies are very orange. IR Pass is just a way to cut through bad seeing issues or when I have to shoot lum in brighter moonlight, because I am about to lose the target for the season.
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ogchicken 0.00
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AstroÅmazer:
e. Color calibration - Spectrophotometric if filter analogue is available else Photometric.

You can find and download .csv files for specific filters that aren't in SPCC by default and add them. For example, I own the Antlia Quadband filter which isn't in SPCC by default, but I managed to add it for all channels. (I use PixInsight, so I only know ho to "add" them in PixInsight, but a quick Google search helped me and I'm sure will help you with this.)
AstroÅmazer:
I haven't tried no dithering with my 585/AM3 rig but I dither every 120s/180s so 4-6 30s exposures. Will try no dither and see how it goes.

The Z5/SW SA GTi setup I use definitely has lots of walking noise. But it is useless trying to dither on the GTi.

I have a very similar setup to yours. The same camera (asi585mc pro), WO RedCat 71, AM5 N, ASIAir.

Your setup is well sampled, considering the bad seeing conditions you mentioned, so dithering might not be required to produce similar results. Give it a try and you will be able to decide what works best for you.

Ari Paulechen Junior:
I think Pixinsight with RC astro plugins would make a good difference in your results,

Also, I completely agree with this.

I understand that PixInsight is 300 Euro (before VAT) and the rc-astro suite is around 200 Euro, but considering how much we spend on our equipment, spending some more on adequate processing software is acceptable in my opinion.
That being said, PixInsight really is an amazing tool for astrophotographers and the rc-astro Blur, Star and NoiseXterminator will 100% help and improve your workflow.

For each of the tools you can request a free trial. For PixInsight you get 45 days of the "full software" (Not a "Trial Version" but everything you would get if you purchased a commercial license) and for the rc-astro tools you can get a 30 day free trial to use in PixInsight. 

Considering this, there is no reason for you to not, at least, give the software a try. If you don't like it or don't want to spend that much money, you can always go back to what you are doing now.

I am much newer to astrophotography than you are, but looking at your photos tells me that whatever you are doing now, you're doing it good.

Hopefully some of this is helpful.
Clear Skies!
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AstroÅmazer 0.00
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Thank you everyone for taking the time to provide all the helpful feedback! It is reassuring to know I am on the right path.
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CCDnOES 8.34
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andrea tasselli:
10. I never dither. Dither is a waste of time.


As with most things, it depends.   With an encoder  system and unguided, dither literally takes only a couple seconds per exposure.
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andreatax 9.89
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Maybe, but how many of us have such a system?
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