Orpington Astronomical Society

Astronomy => Astrophotography => Topic started by: MarkS on Jul 17, 2011, 15:12:48

Title: Lagoon and Trifid from High Halden
Post by: MarkS on Jul 17, 2011, 15:12:48

I took this on 26th June.  I was hoping to make a mosaic but this won't happen now because it's getting too late in the year and I am having an operation on my hand this week which will put me out of action for a while.  So here it is:

Modified Canon 350D on Tak Epsilon ED180 with CLS filter.
18 x 5min @ISO 800 + 5 x 2.5min @ISO 400

(http://www.markshelley.co.uk/Astronomy/2011/lagoon26062011small.jpg)

Larger version here:
http://www.markshelley.co.uk/Astronomy/2011/lagoon26062011.jpg

It has come out much better than last year's version (http://www.markshelley.co.uk/Astronomy/2010/trifid_2010.html) - mainly because the sky background was much darker at HH than at Beachy Head.

Mark
Title: Re: Lagoon and Trifid from High Halden
Post by: JohnP on Jul 17, 2011, 15:20:10
Mark - superb once again - even more so considering the relatively few number of subs. Love the colours & the 'misty' feel to it..

Great,  John
Title: Re: Lagoon and Trifid from High Halden
Post by: mickw on Jul 17, 2011, 16:11:03
Very nice.

Were the shorter, slower subs to save the core ?
Title: Re: Lagoon and Trifid from High Halden
Post by: MarkS on Jul 17, 2011, 17:31:06
Quote from: mickw
Were the shorter, slower subs to save the core ?

Yes.  The burnt out core is one of the (many) disappointing things about last year's version.
Title: Re: Lagoon and Trifid from High Halden
Post by: PhilB on Jul 18, 2011, 06:00:23
Very well done
Title: Re: Lagoon and Trifid from High Halden
Post by: Mike on Jul 18, 2011, 06:56:25
Looks great Mark.
Title: Re: Lagoon and Trifid from High Halden
Post by: RobertM on Jul 18, 2011, 08:43:20
A great result Mark.  It needs a lot more subs to get some detail in the Lagoon Nebula so I hope you get to do those at some point.

Robert
Title: Re: Lagoon and Trifid from High Halden
Post by: MarkS on Jul 18, 2011, 09:55:35
Quote from: RobertM
It needs a lot more subs to get some detail in the Lagoon Nebula so I hope you get to do those at some point.

Extracting detail in the Lagoon is not that easy.  Being so low above the horizon, the light is passing through at least 4 times as much atmosphere as an image taken at zenith - this means that the seeing creates 4 times as much blurring.

The bigger problem I noticed was atmospheric dispersion which "smears" the star colours giving a red fringe one side of the star and a blue fringe the other.  The real problem here was that the amount of smearing changed from sub to sub over the 2 hour acquisition as the height above the horizon and the angle of the target (relative to the ground) changed.

The only way I could process this image was to completely abandon my usual "full-colour stacking" approach and, instead, split up the R,G,B channels and do a full stack on each channel before recombining later into a colour image.  I still have some blue fringing on the stars in the Lagoon - I'm don't know why but at least it is symmetric!

Mark
Title: Re: Lagoon and Trifid from High Halden
Post by: RobertM on Jul 18, 2011, 20:00:47
Well, however you processed it, that was a great result from these latitudes !
Title: Re: Lagoon and Trifid from High Halden
Post by: Carole on Jul 20, 2011, 14:56:00
Oooow, very nice Mark.  (Finally found an internet cafe in northern Majorca ) and this is the first post I´ve seen.  Looks excellent to me Mark.

Carole
Title: Re: Lagoon and Trifid from High Halden
Post by: Fay on Jul 20, 2011, 21:15:14
Come out very well Mark!!!!!!!!
Title: Re: Lagoon and Trifid from High Halden
Post by: MarkS on Jul 24, 2011, 08:51:22

Sitting here with one arm I've done a complete re-process.  Subtle difference but I'm far happier with the result.

(http://www.markshelley.co.uk/Astronomy/2011/lagoon26062011v3small.jpg)

Larger version (2/3 scaled from full size):
http://www.markshelley.co.uk/Astronomy/2011/lagoon26062011v3.jpg

Mark
Title: Re: Lagoon and Trifid from High Halden
Post by: Fay on Jul 24, 2011, 09:09:51
yes, like that Mark, more definition & contrast
Title: Re: Lagoon and Trifid from High Halden
Post by: PhilB on Jul 24, 2011, 09:12:51
Spent a while jumping from one version to the other. The contrast increase has certainly made the detail in the image easier to see. Nice reprocess!
Title: Re: Lagoon and Trifid from High Halden
Post by: mickw on Jul 24, 2011, 10:21:52
Looks much better.

Nice work lefty  ;)
Title: Re: Lagoon and Trifid from High Halden
Post by: The Thing on Jul 24, 2011, 23:54:26
Excellent stuff. Such expertise is hard won but pays dividends, plus having some time on your hand helps!
Title: Re: Lagoon and Trifid from High Halden
Post by: Whitters on Jul 25, 2011, 23:18:02
Fantastic! love the Bok globules in M8 and the dust clouds in the Milky Way. Wonderful image.
Title: Re: Lagoon and Trifid from High Halden
Post by: RobertM on Jul 26, 2011, 21:11:28
Nice reprocess.  There is a lot more contrast and the stars don't seem to have suffered at all.

Robert