M20 Trifid Nebula in LRGB and Ha LRGB ( Sydney Bortle 8 )

[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 or Ha LRGB image.

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.

Links to Astrobin below for full resolution…….,

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

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

Attached original frame versions , Crop frame and Super Crop versions in LRGB and Ha LRGB ( IIS 200Kb limits )


Thanks for looking

Comments welcome

Martin

[strongmanmike]

Bortle 8 huh..? :eyepop: Man, Chuck Connors eat your heart out, Martone is the real Thrillseeker (https://youtu.be/jQFK7Fd2O6A)!

Seriously though, pretty damn good considering where you captured from, nice work mate.

Mike

[CaptainCook]

I like the stars. I just ''made'' some like that tonight (for my pillars of creation pic) using old sparklers.

[alpal]

Hi Martin,
nice picture but there appears to be a problem with the black point.
Some parts are way down at 1 or 2 out of 255 bits.
Most people would aim for a black point of between 20 and 30 bits.

It appears that the black point has been clipped when the image was stretched.
I attach a picture of the Photoshop Histogram of your picture on the left of M20
and another of a random picture of M20 found on the internet on the right.
The Histograms shows the problem.
Louie Atalas gives some very good explanations of Histograms here:
https://www.youtube.com/watch?v=IllEy85eUWY
and here:
https://www.youtube.com/watch?v=fE2GS_87Ct8

Free programs like NASA FITS Liberator
https://esahubble.org/projects/fits_liberator/download_v30/
take all of the hard work out of stretching and when I was imaging
I used it all the time.
I found that the stretch function of x^(1/5) was very good
at getting high compression to cover the whole 255 bit range
once the picture ended up as a jpg.

I hope I have been of help to you?


cheers
Allan

[Startrek]

Thanks Mike, Gary and Allan

Allan,
Yes I was aware it’s slightly black clipped and it wasn’t caused by stretching.Stretching in Startools “will not” clip your data.
Probably in the process of dampening down the extremely bright busy star field.Maybe I should have used Star reduction in lieu of the Isolate algorithm.I’ll have another go at it !!
StarTools isolate algorithm in Super Structure was probably the culprit.
Thanks for highlighting that issue.

Cheers
Martin

[Dave882]

Beautiful mate thats a fine Trifid!! I really like the addition of the Ha - I think it really adds something to overall appeal. I can certainly sympathise with your LP struggles - and data management is one of those aspects of astro that you never really consider when you're first getting into it!!!

I've found the Sydney conditions really difficult recently with heavy dew and lots of fog/mist even when otherwise clear. Great effort to come out with such a great image.

[Startrek]

Gee thanks Dave,
Lovely comments
Pretty happy with the Ha accent image too.
30 sec subs are my sweet spot now on broadband targets during New Moon
I do agree with Allan though , I pegged back the background a tad too much which has reduced some fine detail in the Star field and main body of the Trifid.
I’m definitely going to revisit, re process and repost , the data set is worth spending time on
Also I totally agree with seeing in Sydney , it’s been ordinary through Winter. I’ve been using a pedestal fan to blow air over my rig plus switch my heaters on to avoid cutting my sessions early.
My sessions have been dew free on the mirrors and lens to the early hours.
Thankfully I’ve only discarded a small amount of subs due to satellite trails , cloud and aircraft Oh and the odd minor Ra or Dec excursion in guiding etc…
Thanks again
Martin

[alpal]

Martin,



Thanks Martin,
I look forward to seeing your re-process -
and yes it is worth it with such good data. :)



cheers
Allan