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RCC - Iris Nebula - image capture and processing - A long list of issues!! :-)

Request for feedback NGC7023 NGC Objects Deep Sky Nebula
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Aaron Thompson avatar
Aaron Thompson avatar
Iris nebula



Iris Nebula


ES ED80
Guided
Nikon D5500 unmodded


Seeing was poor but I do not blame this on my noise or bloated stars.

What I am looking for are comments that can help correct underlying issues.
Image is cropped, i have a field flattener on the way so lets not worry about the stretched stars on the corners.

I was too heavy on the background removal in PI
According to DSS my FWHM was in the 8-9 which i believe is failure level bad.

Stars seem over saturated as well, but i would like to increase my exposures to up to 180 or 300s.  The saturation would get even worse correct? Its cloudy right now so i cannot run tests at this time.

Others are able to produce nice definition between the dark nebula and the background star field.  I suppose that as i was trying to eliminate noise I have killed part of the surrounding nebula so it is less distinct against the stars.

Bortle 8, no filters used.

Thanks for any advise! 
Cheers
Aaron
Damian Russo avatar
Damian Russo avatar
I have had a lot of issues imaging this nebula. Check out my image that I uploaded to astrobin. This was 6 hrs of integration using a triad quadband band filter. I think my stars are pretty good, but I think more integration is needed. Also, I think my subs are 5 minutes. The first time I tried it was with 3 minute exposures and it came out terrible. I am sure that people will give you some good pointers.
andrea tasselli avatar
andrea tasselli avatar
Focus control is key here and needs to be kept in check at all times.  That's issue n.1.
2nd is ISO/exposure. Stick with 200 ISO and 180s.
3rd you need way longer integration time than just 3h with a DSLR.
I strongly suggest you get a proper LP filter (say a L-PRO) if you shoot in Bortle 8 skies. That is going to help enormously.
I don't think you overdid the BG removal, there isn't just not enough signal as it is to bring out the fainter stuff, given also the condition you shooting in, the small aperture and the poor focus.
You could remove the green cast of the background by using the right tool in PI.
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Aaron Thompson avatar
Aaron Thompson avatar
Great feedback, thank you.

I am going to restart this target at 180s exposures and make sure my focus is sharp.  With the DSLR and not being able to see the stars in live view makes this more difficult then I would like.

I have a Baader LPS filter but it is 1.24 inch and I am imaging with a 2inch Adapter to reduce vignette.

Would you recommend I work through the vignette at this time at 1.25inch with the filter or continue without the filter and image with a 2inch clearance?

Next I am going to sit on the target for several nights.  I want to work out a target total exposure time.  If 3 is just not enough, and I try to follow the rule of squares then maybe I should run a trial to clear 9 hours and see what happens?

Much Appreciated
andrea tasselli avatar
andrea tasselli avatar
If your aren't using APT I'd advise you do. Obviously you need a laptop of some form to go with it. In it you'd find a numer of tools to help you out with the focusing routine. If you can't, for whatever reasons, than the trick here is to do the focusing on a brighter star where you can see how your focusing goes on the live preview. Or use a Bahtinov mask made to the specific of your focal length.

Don't use a 1.25" filter as it would step down your aperture or massiveky vignette the sensor. Still the suggestion to get a 2" LP filter stands. You would probably need at least around 12 hours for a subject like NGC7023 in skies like yours.
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Aaron Thompson avatar
Aaron Thompson avatar
Ok point well taken.  I suppose your concern over the Light pollution filter would apply to any target, and due to Christmas for the family i doubt my LPS filter will make the list!  LOL 

Maybe a different target would be in order that is less susceptible to the pollution for completing this practice and producing an image with reasonable quality.


For example, Elephants trunk nebula is in a good place for me.  I want to practice going for longer exposures on nebula's instead of switching type to a galaxy or globular,   M33 (fits better in the camera frame then M31)  Maybe the flaming star nebula.  no globular clusters are visible for me. 

But to not beat a dead horse  maybe a type switch is best.   Once my field flatterer arrives i will target Pleiades  early next month.

Thank you again for the comments.
Torben van Hees avatar
Torben van Hees avatar
If you want to shoot emission nebulae, an unmodded DSLR will do very badly, especially in light pollution, filters will not help much because the camera has low sensitivity for the hydrogen emissions. A modified DSLR (or dedicated/cooled astro camera) will benefit from LP/narrowband filters. For broadband targets (like the Iris), I found that the LP filters don't work well for me in Bortle 6: You get color shifts and loose enough signal due to the filtering that it's not really helpful.
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Aaron Thompson avatar
Aaron Thompson avatar
Ok, this is interesting.

Without a filter, and why not test to see where i can get without one right.  A Proper process is still a good process even if the equipment is not up to par. 

I am considering weather or not i can astro mod my camera myself.  Maybe..

If i do astro mod then i will need some 2 inch filters so that i can control IR or Non IR imaging.

I feel like I am a few good practices off really making some good work with the equipment i do have.

Under the conditions that I have being in a high bortle zone, what targets do you think would be best case targets for my equipment?

Thanks
Aaron Thompson avatar
Aaron Thompson avatar
Another thought Torben!

I was just looking at your images and noticed on your image of the needle galaxy.  Fantastic by the way.

As a process i noticed you would take both 90s and 180s images in each band. 

Can I assume that this is to preserve star color?
When you combine your images do you stack these exposures separately? And if so how do you combine them afterwards? Photoshop?

If you were to recommend other readings or content to learn how to handle doing that where would you send me?

Thank you!
Aaron
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Torben van Hees avatar
Torben van Hees avatar
Another thought Torben!

I was just looking at your images and noticed on your image of the needle galaxy.  Fantastic by the way.

As a process i noticed you would take both 90s and 180s images in each band. 

Can I assume that this is to preserve star color?
When you combine your images do you stack these exposures separately? And if so how do you combine them afterwards? Photoshop?

If you were to recommend other readings or content to learn how to handle doing that where would you send me?

Thank you!
Aaron

Thanks for the compliment!

Nothing as fancy. I modified my Heq-5 during that time and realized I could take longer subs. I experimented around with gain and sub length and different integrations to see if I could eek out a bit better SNR (I couldn’t, at least not in broadband). Stars weren‘t burnt out in any of the subs. In the end, I just stacked everything in Pixinsight. If you weigh the subs by noise estimate, it works very well. If you want to combine long and short subs where the long subs have burnt out areas, you have to use a HDR process. I don‘t have much experience with that, unfortunately. Also, my knowledge of Photoshop is rudimentary. I do most processing in PI and sometimes very little touching up in Lightroom or Photoshop.
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andrea tasselli avatar
andrea tasselli avatar
Torben van Hees:
If you want to shoot emission nebulae, an unmodded DSLR will do very badly, especially in light pollution, filters will not help much because the camera has low sensitivity for the hydrogen emissions. A modified DSLR (or dedicated/cooled astro camera) will benefit from LP/narrowband filters. For broadband targets (like the Iris), I found that the LP filters don't work well for me in Bortle 6: You get color shifts and loose enough signal due to the filtering that it's not really helpful.

That is not accurate. I'd say that a LP suppression filter is even more  necessary in a heavily LP'd environment with unmodded DSLR  as what little Ha emission is there benefits from whatever help it can get. Opposite to what you've found I find that my L-PRO helps out in my Bortle-6 sky even with broadband subjects. And there are no colour shifts.
Aaron Thompson avatar
Aaron Thompson avatar
For stacking is have been using Deep sky stacker.   Would you guys recommend learning the process in PixInsight?  Is it worth the extra effort?
andrea tasselli avatar
andrea tasselli avatar
PI costs money. It is worth the investment in both money and time if you're going for the long run, otherwise you'll be better off learning to use Siril. It costs nothing and it is very good.
Torben van Hees avatar
Torben van Hees avatar
andrea tasselli:
Torben van Hees:
If you want to shoot emission nebulae, an unmodded DSLR will do very badly, especially in light pollution, filters will not help much because the camera has low sensitivity for the hydrogen emissions. A modified DSLR (or dedicated/cooled astro camera) will benefit from LP/narrowband filters. For broadband targets (like the Iris), I found that the LP filters don't work well for me in Bortle 6: You get color shifts and loose enough signal due to the filtering that it's not really helpful.

That is not accurate. I'd say that a LP suppression filter is even more  necessary in a heavily LP'd environment with unmodded DSLR  as what little Ha emission is there benefits from whatever help it can get. Opposite to what you've found I find that my L-PRO helps out in my Bortle-6 sky even with broadband subjects. And there are no colour shifts.

I don‘t think we‘re in disagreement here. I‘m not saying the LP filters don‘t help - but considering the bad efficiency of an unmodded DSLR in LP I think the better way to image those targets is to get a Ha-sensitive camera, drive to darker skies and especially gather more total integration: For the Iris nebula I needed 4h in Bortle 4 for a decent image. In Bortle 6, 10h was by far not enough, I would guesstimate 20 to be needed. 

If the LP filters help or not is dependent heavily on the kind of LP and the filter, so YMMV. I’ve tried both the L-Pro and the Astronomik CLS. While both suppress some LP so I can expose longer, the integrated stacks had less SNR than the ones with a regular UR/IV-cut for broadband. The CLS made color calibration quite difficult for the Leo triplet in my gallery.

For emission targets, both filters were helpful, but a dual-narrowband would be even better.
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Torben van Hees avatar
Torben van Hees avatar
andrea tasselli:
PI costs money. It is worth the investment in both money and time if you're going for the long run, otherwise you'll be better off learning to use Siril. It costs nothing and it is very good.

I really like the options PI gives you for the whole workflow. But it is not something for quick results. For a lot less money, I find Astro Pixel Processor to have excellent preprocessing and an accessible UI, especially for multi-night sessions or mosaics. Postprocessing is comparably limited. I wouldn’t really get PI just for calibration and stacking.
I can’t comment on Siril. I used it early last year and didn’t like its workflow, but there is a new UI out for it now.
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