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PixInsight => Gallery => Topic started by: troypiggo on 2011 August 02 15:34:40

Title: M20 Trifid Nebula - a couple of firsts
Post by: troypiggo on 2011 August 02 15:34:40

G'day all.  This image is a few firsts - my first processed with PixInsight, and my first LRGB image taken with mono CCD camera.  What a learning curve that was!  I now also have a million questions, so expect an onslaught of posts from me here in these forums shortly  :)

Please, if you see any defects or have any advice, I'd really appreciate it.

(http://farm7.static.flickr.com/6016/6000998371_2ed8b0c7d3_z.jpg) (http://www.flickr.com/photos/troypiggo/6000998371/)

Title: Re: M20 Trifid Nebula - a couple of firsts
Post by: Nocturnal on 2011 August 02 17:22:06

Looks good to me! It appears you did not upload a 1:1 version so it's hard to give an opinion of the star field. The stars appear a bit out of round here and there. Can you share a few details about the scope, camera and acquisition?

Title: Re: M20 Trifid Nebula - a couple of firsts
Post by: troypiggo on 2011 August 02 17:39:06

Thanks mate!  Wasn't sure about the image posting limits here, so only linked this 640px version.

You're right, there are some stars that are out of round in there when viewed at full scale.  Not sure how to round them up.  The scope is a 10" Newtonian and I use a Baader MPCC coma corrector.  I haven't been able to pin down the source of the out of shape stars - whether it's still coma, spacing between MPCC and camera (although I have a 10mm spacer there that should theoretically be correct with my QSI583ws), camera not sitting square in focuser, guiding errors, or rotation due to slight polar misalignment around the guide star, or a combination of the above.  I'll need to experiment some more.

They're all eggy in different directions.  Any tips on rounding them up?

Acquisition was 12x4min L, and 10x1min 2x2 binned for RGB, with flats and darks applied.

Title: Re: M20 Trifid Nebula - a couple of firsts
Post by: Nocturnal on 2011 August 02 17:42:40

Hi,

file size is limited here but maybe flickr allows larger images? That's where I looked and the largest wasn't 1:1 I'm pretty sure.

Getting round stars is pretty tough, especially with newtonians. You may have reached the maximum possible with an MPCC. The trick is to find the source without buying every part of the shelf. First make sure you don't have differential flexure, then try to vary the distance between MPCC and camera.

Title: Re: M20 Trifid Nebula - a couple of firsts
Post by: Lex on 2011 August 09 14:11:36

Hi,

have you tried to play a bit with your mounts guide aggressiveness;  lowering or lifting these values often helped me out.
If this artifact occurs in my images i do also opt for more shorter exposures rather than some longer ones; the stars then have less choice the be pulled to an "eggform"

By the way; i like your pic!

Cheers

Lex

Title: Re: M20 Trifid Nebula - a couple of firsts
Post by: troypiggo on 2011 August 09 15:38:38

Thanks Lex!

I have played with the guiding aggressiveness.  I don't think it's a guiding problem as the stars "out of shape" is in different directions.  I think it's some fine-tuning of my camera/MPCC spacing that I need to work on as Sander has suggested.