IC 4628 Prawn Nebula

[Startrek]

I haven’t image the Prawn Nebula since 2022 and back then I was using my 2600MC OSC. The Prawn Nebula was well placed throughout May and captured around 10 hrs of data over 3 nights using my 2600MM and Antlia 3nm SHO filters.Most of the data was captured during a waning moon.

Captured over 3 nights ( 10 hours integration)
Waning Moon 75% to 25%
Seeing conditions poor to average ( high humidity )
Heavy dew after 9pm on all 3 nights
Bortle 8 City suburban skies
8”f5 Klaus Helmerich Carbon fibre Newtonian Reflector
Skywatcher EQ6-R pro mount
ZWO 2600MM cooled to -10C , Gain 100
ZWO 7x2” EFW
ZWO EAF
Orion 60mm guide scope with helical focuser
ZWO 120MM guide scope
PHD2 Multistar guiding ( total error avg 0.50 to 0.60 arc sec )
Antlia 3nm Filters
Ha 75 x 3min dithered subs
Oiii 60 x 3min dithered subs
Sii 62 x 3min dithered subs
Darks frames from Library
Flats Ha , Oiii and Sii
Flat Darks Ha, Oiii and Sii
Analysed , Calibrated, Stacked and Aligned in ASTAP
Processed in Startools V1.8 via Compose
Colour HST / SHO preset with saturation and colour bias adjustments
Didn’t capture RGB stars , instead used Startools Shrink module with a Star mask and adjusted colour taming and halo extend parameters. Not perfect but Stars are good enough for me considering it’s an SHO palette.
All 3 nights had heavy dew setting in early ( around 9pm ) so used my Kendrick heater band on the guide scope which works a treat but heater bands on carbon newts don’t work very well , so decided to use my 400mm pedestal fan and blew air over the Newt all night. It worked surprisingly well and allowed me to image through to the early hours. I didn’t think it would work but it did , and over 3 different nights where humidity was above 85%. That old fan is now apart of my Astro kit.

Quite pleased with the final image considering condition's

In regard to processing in Startools , I found that on very rare occasions ( where noise is problematic) using Digital Development in lieu of AutoDev has produced a better overall result for your final stretch in preparation for the next modules. This project is one of those occasions.
I tried everything in AutoDev to provide a smooth low noise contrast from the main structure of the nebula to the fainter outer nebulosity areas but they kept ending up too clumpy. Yes I did use a ROI adjust ignore fine detail parameters and adjust gamma etc …,
Digital Dev allowed me to gradually stretch the main object whilst keeping the outer areas with smooth transition. I agree it’s not the most appropriate way to stretch the image and provide a better dynamic range of tones and contrast , but as far as my eyes are concerned, Digital Dev did a better job and more pleasing to the eye.
Just thought I’d mention it.
Also SV Decon worked so much better with a Digital Dev stretch than an AutoDev stretch. Star cores did not turn into coalesced super bright squares , they looked more natural IMO .

Attached images at reduced res
Full size with cropped edges
Crop version for a close look

Link to Astrobin below for 100% resolution ….,

https://www.astrobin.com/j4c5ig/

Comments welcome
Thanks for looking
Martin

[decay]

Hi Martin,

All of your last images are of excellent quality. Seems that you figured out everything to perfection.

And thanks for mentioning your experience using AutoDev vs. FilmDev in this case. Very interesting. I guess we will have some more discussions regarding OptiDev ... but I hope this is a way to help Ivo to optimize all this stuff.

Fascinating story featuring your old fan Dew is most times a huge problem for me, too. I built a dewcap out of cardboard (which is quite vast for an 8" newt) and this works quite well. But there have been some strange gradients in my last image and I suppose, the dewcap caused this. I will have to re-think this. One other possibility is to use a heating attached to the secondary mirror. Stefan built such a heating DIY, if I remember correctly.

https://www.teleskop-express.de/en/tele ... older-7324

Best regards, Dietmar.

[Startrek]

Hi Dietmar,
Thanks for your kind comments, much appreciated
Yes it’s very gratifying when you build your own scope and put it good use( I just bought the carbon tube from Klaus Helmerich and drilled out and fitted my own mirrors , spider , focusers and so on…. Did the same for my 10” Carbon Newt in my Dome down south ) Conditions weren’t great but had enough data to tweak and end up with a respectable image.
I failed to mention that our City ( Sydney) has been lit up for 2 weeks in a spectacular event called “Vivid” which did add gradients to my subs. It was noticeable from my backyard looking north as I’m only 20km from the City centre.
Thanks for the tip regarding dew straps , I’ve been using a Kendrick ( Canadian product ) secondary mirror dew strap on my 12” Goto Dob for visual observation for many years.
In regards to dew, I find the primary mirror is the one that ends your session before the secondary as my secondary is facing downwards most of the time ( camera pointing to the ground in park or home position)
In any case the old fan worked well to sustain my sessions but may be a different case mid summer ( we are in Winter at the moment )
I’m still using ST 1.8 and apologies for it calling Film Dev as it use to be called Digital Dev in ST 1.3 , 1.4 …….
I guess having AutoDev and Film Dev gives you flexibility, I just couldn’t get AutoDev to work on this image and usually I can harness its excellent performance.
From past posts I know Ivo always recommends folk to use AutoDev ( Opti Dev ) but we are our own judges I suppose. What ever works go with that option
Thanks again
Martin