M8 Lagoon Nebula under Bortle 8 Skies

[Startrek]

After recently having my ZWOASI2600MC repaired under warranty ( silicon grease smeared over sensor from thermal pad ) I decided to test the repaired camera on a big bright nebula under my light polluted skies
M8 Lagoon Nebula under Bortle 8 and 32% waxing moon
Scope: 6” f6 GSO newtonian reflector
Mount : Skywatcher EQ6-R pro
PHD2 guiding
2 hours ( 3 minute dithered subs )
Imaging Camera: ZWOASI2600MC
Filter: Optolong L Extreme
Goto and tracking EQMOD and Ascom Stellarium
Captured with APT

Stacked in DSS
Processed in Startools V1.7 Linear data set OSC

Native frame version
Cropped framed versions to show close up detail

Thanks for looking

[Stefan B]

Wow, that looks really great with an amazing amount of detail! It is especially good in some aspects with which I am frequently struggling. May I ask some questions on the aquisition and processing procedure?

My images often have halos around bright stars with spikes. See this for example: download/file.php?id=2229 Look at the bright blue stars with spikes. I think using Reveal All or Optimize in the HDR module makes it worse, but these haven't been used here. It's probably real signal coming from my optics. You are using a 6'' Newton similar to mine, but your bright stars with spikes look perfect. May I ask which Coma Corrector you are using? Are taking particular measures during post processing in order to get rid of these artefacts or don't you see this in your datasets at all?

Moreover I am interested in the colors of your image. They look great and very natural to me. I am wondering which color scheme you used in the color module since the data has been aquired with a duo NB filter. My l-eNhance filtered images tend to show very blue stars and a red for the nebulosity which I don't quite like. Usually I then go for H(HO)O recombinations resembling the Hubble palette. Can you tell how you processed the colors? I am really interested.

Thanks in advance and once again: Awesome image and crops!

Best regards
Stefan

[Startrek]

Stefan,
I use a Baader MPCC Mk3 coma corrector
Here’s my workflow from “memory” on my image of M8 Lagoon Nebula (settings may be slightly different) -
Load data set
Select centre tab ( Linear from OSC/ DSLR with Bayer matrix and not white balanced )
AutoDev ( first stretch to inspect data )
Bin 50% default ( my image scale is 0.88arc sec per pixel, so over sampled therefore ST binning works well )
Crop ( crop perimeter to centre object and stacking artifacts )
Wipe ( Narrowband preset , increase dark anomalies to 4 pixels )
AutoDev ( final stretch , select ROI around nebula and increase ignore fine detail to 4.5 pixels , increase Shadow Linearity to 60% , remainder default )
Star Mask ( Stars 8 / 2 ) grow and invert so stars are well covered and are not sampled ( ie white )
Contrast ( Locality 30% , Shadow Dynamic Range 30% Brightness retention off , Expose dark areas yes )
HDR ( Reveal DSO core 1.2 pixels , Optimise Hard 2 pixels )
Decon ( increase primary radius to 2.5pixels ) takes 2 minutes to deconvolve
Shrink ( invert Star mask so only stars are sampled ) use Tighten default 10 pixels
Clear Mask
Colour ( select Bi colour preset ) Reduce Sliders - increase green to 4.0 , increase red to 2.0 , increase blue to 1.50 ( these might have been a bit higher or lower ??? I can’t exactly remember )
Leave main Saturation at 200% , Adjust bright saturation to 2.5 , adjust dark saturation to 2.5
Star Mask ( Stars 8/ 2 ) grow and invert so stars are well covered and not sampled ( ie white )
Super Structure ( Power of Inverse , Gamma 0.50, Brightness Colour Both , Saturation 40% , Detail Preservation Linear Brightness Mask , Strength 150%, Brightness Retention Off
2nd Super Structure ( Isolate ) 25%
Tracking and Noise Reduction ( default ) usually 5.0 to 6.0 pixels
Save completed image

Stefan,
Your attached image shows shorter diffraction spikes typical of a faster newtonian ( ie f4 )
What is you focal ratio in your 6” ?
Also what camera are you imaging with ?
My stars tend to be greenish when using the L Extreme but I have no issue at all adjusting them back to natural colours
When not using the L Extreme filter in a different imaging location ( Bortle 3 ) under dark skies I usually colour my stars separately with a star Mask after completing the Colour of the main object ( it takes a bit of skill to set a nice tight star mask to colour the stars correctly without it being to noticeable) I use the Lassoo preset to assist in that
Hope the above information is helpful
Clear Skies

[Stefan B]

Hi!

Thanks so much for your detailed reply and workflow!

I use a Baader MPCC Mk3 coma corrector

I use the same CC, great information!

What is you focal ratio in your 6” ?
Also what camera are you imaging with ?

Mine is a f5. I missed that yours is f6. That might well make a difference. The camera I use is a modified (full spectrum) Canon 1100d. When not using the l-enhance I use an UV/IR cut filter.

My stars tend to be greenish when using the L Extreme but I have no issue at all adjusting them back to natural colours

If I understand your workflow correctly then you are not altering the colors of the stars independently of the DSO when using the l-extreme, right? If you push your stars to be white, you also push back the OIII color information... I will try your worfklow at the next opportunity and see what I get!

Thanks and best regards
Stefan

[Startrek]

Stefan
Glad to help
Just remember our cameras are chalk and cheese , your 1100D DSLR camera modded is a 12 megapixel camera with 9 stops of Dynamic Range and an overall Quantum Efficiency of only 36%
My ZWOASI2600MC is a 26 megapixel camera has 14 stops of Dynamic range and an overall Quantum Efficiency of over 80%. This camera has almost zero amp glow and rarely requires darks
My ZWO camera has a greater contrast of width in greyscale and therefore when the colour algorithms are applied there’s more depth in the data across the spectrum
My ZWO camera also has an in built UV/ IR cut filter which also reduces halo and Star bloat too
I hope you resolve your Star colour issues,
NB: I used a Canon 600D for 4 years in the same scope and never used a NB filter so struggled with imaging under my heavy light polluted skies. I still use the Canon but only for dabbling in lunar and planetary imaging
Does your 1100D have a UV/ IR filter ?
Clear Skies
Martin

[Stefan B]

Hi Martin!

Just remember our cameras are chalk and cheese , your 1100D DSLR camera modded is a 12 megapixel camera with 9 stops of Dynamic Range and an overall Quantum Efficiency of only 36%
My ZWOASI2600MC is a 26 megapixel camera has 14 stops of Dynamic range and an overall Quantum Efficiency of over 80%. This camera has almost zero amp glow and rarely requires darks

Completely right. But if your optics would suffer from the same problem, your camera should easily pick it up

Does your 1100D have a UV/ IR filter ?

Not any more, it's modded. If not using a duo NB filter, an Optolong UV/IR cut filter threaded in front of the MPCC protects the sensor. But UV/IR light shouldn't be that big an issue for Newtonians anyway, since it doesn't suffer from chromatic aberration, right?

Regards
Stefan