M20 Trifid Nebula LRGB and LRGB with Ha Accent

[Startrek]

My first clear new moon period so far this year so took the opportunity to image one of my favourite broadband targets , M20 Trifid Nebula, under City Suburban Bortle 8 light polluted skies. Imaged over 4 nights with poor to average seeing conditions.
Due to heavy light pollution I opted for short subs ( 30 sec )
I also captured Ha data as well to create my first Ha LRGB image.
8 hrs LRGB total integration
2 hrs Ha data

8”f5 Klaus Helmerich Carbon fibre Newtonian Reflector
Skywatcher EQ6-R pro mount
ZWO 2600MM cooled to -10C , Gain 0 LRGB , Gain 100 Ha
ZWO 7x2” EFW
ZWO EAF
Orion 60mm guide scope with helical focuser
ZWO 120MM guide camera
PHD2 Multistar guiding ( total error avg 0.50 to 0.60 arc sec )
Antlia LRGB Filters and Ha 3nm filter
Lum 450 x 30 sec subs
Red 190 x 30 sec subs
Green 180 x 30 sec subs
Blue 180 x 30 sec subs
Dithered every 3rd Sub
Ha 42 x 180 sec dithered subs
Darks frames from Library
Flats LRGB and Ha
Flat Darks LRGB and Ha
Analysed , Calibrated, Stacked and Aligned in ASTAP
Processed in Startools V1.8 via Compose L + Synthetic L RGB , RGB.
Created both an LRGB image and a LRGB with Ha Accent

Under my heavy light polluted skies imaging broadband targets during the new moon period has been almost a waist of time due to the any usable signal being swamped with noise ( gradients). When the moon is up it’s a definite waist of time.
However this time I used really short 30 sec subs at Gain 0 on the 2600MM and for 8 to 10 hrs of data the initial Auto stretch was remarkably clean with some excellent detail. Gives me confidence in the future now during new moon periods.
The downside is that I had to capture over 1000 subs with sub file sizes of 51MB.
My Lappy, stacking software ASTAP and post processing software Startools did and excellent job of handling the data load.

Attached versions reduced resolution

Links to Astrobin for full resolution……,

https://www.astrobin.com/rde4nn/

https://www.astrobin.com/j05tfu/


Thanks for looking

Comments welcome

Martin

[Startrek]

More Crop versions
Thanks for looking

Martin

[admin]

Fantastic use of the NBAccent module. Clean, informative; love it!

[Startrek]

Thanks Ivo,
I thoroughly enjoyed processing my first LRGB with Ha accent
I’ll be honest I didn’t use the Nebula preset ( Red/ Purple) instead I preferred to use the Galaxy preset ( Red ) as the accent colour seemed to blend in better with M20

Here’s a reprocess for both LRGB and LRGB with Ha accent using a larger ROI during the AutoDev
It definitely exposed a bit more detail.

Links to Astrobin below ………,

https://www.astrobin.com/rde4nn/

https://www.astrobin.com/j05tfu/

Thanks for taking the time to comment

Clear Skies
Martin
aka Startrek

[Startrek]

Some attached crop versions of the LRGB and LRGB with Ha accent revisions

Clear Skies
Martin

[decay]

Hi Martin,

so much versions I really like the Ha versions. It looks like the nebula is glowing from inside. And I nearly can't believe that this is from a Bortle 8 site. There's so much detail visible in the dark clouds in the centre of the nebula.

However this time I used really short 30 sec subs at Gain 0 on the 2600MM and for 8 to 10 hrs of data the initial Auto stretch was remarkably clean with some excellent detail.

Yes, I also have the impression, that using short subs is helpful under heavy light pollution. When I started with AP - without guiding - , I only was able to take short subs and the results were surprisingly good. With guiding, I switched to longer subs, but shorter subs seem to work somehow better and so I went back to short subs. Yep, a lot of data to store and to stack, but I think it's worth it.

Best regards, Dietmar.

[Startrek]

Hi Dietmar,
Thank you for your reply and comments
Much appreciated
Whilst very happy with these results and also for Ivo’s lovely comments, I wasn’t entirely please with the color.
The reds were too pink and the blues were too purple
So I reprocessed the image and posted my final version a day later. The color in the final revision is much more traditional and pleasing to the eye IMO.
Folk on my local forum have mentioned over the years that by background is too dark ( almost black clipped ) I assured them that Startools will not allow you to clip your data unless you set your influence to 0%.
One of our members used my image and ran it through a software program with conventional histogram levels and curves and found some areas of my image were reading only 3 or 4 ( 0-255 ) so very close to black clipped.
So I’ve taken their advice and have now increased “Outside Region of Interest” influence from default 15% to anywhere between 30% to 50%. This has lifted my background slightly and also exposed more detail as well. Obviously the value is proportional to the noise floor or SNR quality of the data.

In regards to sub exposure times with my ZWO 2600MM this is what I use at my two locations -

City suburban Site Bortle 8 skies
ZWO 2600MM -10C , Gain 0
Broadband LRGB ( no moon ) 30 sec subs ( minimum of 8 hours data )
Broadband ( Moon up ) I don’t bother imaging

ZWO 2600MM -10C , Gain 100 HCG
Moon or no moon
Narrowband SHO, HOO etc … ( 3nm filters ) 3min to 5 min subs

Rural Site NexDome Obs Bortle 3 Skies
ZWO 2600MM -10C , Gain 0
Broadband LRGB ( no moon ) 60 to 120 sec subs ( minimum 5 hours data )
Broadband ( Moon up ) I don’t bother imaging

ZWO2600MM -10C , Gain 100 HCG
Moon or no moon
Narrowband SHO , HOO etc… ( 3nm filters ) 3min to 5 min subs

So moving forward I’ll be using 30 sec subs for all Broadband imaging at my City suburban B8 site

One other point to make is that ever since I’ve been imaging Mono ( since August 2023 ) I’ve switched stacking from DSS to ASTAP. ASTAP is far superior than DSS in every facet in regards to Mono imaging. I used DSS for 5 years from my DSLR to my 2600MC with satisfactory results but with Mono , DSS struggled, ASTAP always gave me superior results. I did stack Mono using both DSS and ASTAP for about 3 months then jumped ship to ASTAP.
Cleaner lower noise stack
No calibration issues at all , field is flat and even
For stacking multiple nights , no need for a reference frame etc.. a far simplified process
Although I haven’t stacked OSC with ASTAP as yet but I’m sure it will do a good job.

Thanks again

PS: Have a look at my M20 final revision

Clear Skies
Martin

[decay]

I reprocessed the image and posted my final version a day later.

Have a look at my M20 final revision

Hi Martin,

I forgot to mention, that my comments refer to the lasted revisions you posted on AstroBin - sorry. I replied to this thread because of the points you mentioned here.

Folk on my local forum have mentioned over the years that by background is too dark ( almost black clipped ) I assured them that Startools will not allow you to clip your data unless you set your influence to 0%.
One of our members used my image and ran it through a software program with conventional histogram levels and curves and found some areas of my image were reading only 3 or 4 ( 0-255 ) so very close to black clipped.
So I’ve taken their advice and have now increased “Outside Region of Interest” influence from default 15% to anywhere between 30% to 50%. This has lifted my background slightly and also exposed more detail as well. Obviously the value is proportional to the noise floor or SNR quality of the data.

I think this is an old and recurring topic for us ST users. I'm sure, ST does not clip the data, but it is designed to work without offset to 0. (This is true at least for OptiDev - FilmDev lets us set the SkyGlow.) If we compare other traditionally processed images to images produced by StarTools, the background is often much brighter. This seems to be easier to the eye, but more important it is an advantage if the display(s) which are used are not well calibrated. In my experience especially the dark parts never look the same on different displays. But if we now force OptiDev to push the background, the noise often gets amplified to much and the background gets mottled, undulant or harsh. Sometimes it works well (like it now did for you ), but other times the result remains unpleasant.

Best regards, Dietmar.

[Startrek]

Hi Dietmar,
Thanks again for your comments
I haven’t upgraded to V1.9 as yet so not to familiar with OptiDev but I do agree that attributing more DR ( influence) outside the ROI requires careful analysis based on the noise floor level , quality of calibration and brightness of your target object. I’m just happy staying with v1.8 for the moment.
A final point I’d like to make is that I’m getting much better results with SV Decon now after struggling with it just over a year ago. Again it requires careful analysis and experience with your data to know how hard you can apply this fantastic algorithm.

Really enjoying my Mono journey at both my City suburban site and Rural site. We just don’t get enough clear sky time on the south eastern coast of Australia ( averaging 3 to 4 clear nights a month ) Central regions of Australia experience more like 5 to 10 clear nights a month on average, sometimes more.

Clear Skies

Martin