Updated - IC405 Flaming Star Nebula - 26 Nov 2011 02:30 - Rother Valley Campsite

[The Thing]

I can see both images now.

Are both images linked to in this thread?

Yes. The small version is embedded using the IMG tag.

[MarkS]

I meant the 2 different images - the one before and the one after reprocessing.

I wanted to see if the strange noise pattern was also in the image previous to reprocessing.

[RobertM]

Hi Duncan,

That's a very good attempt at a very difficult target even for a cooled mono camera (well I find it so).

Are you going to add more subs at some point ?

Robert

[The Thing]

I have some subs taken in Beckenham before DSC so I may process and add them.

Originals:

Full Size

[Carole]

That re-process looks much better Duncan, where has all the noise gone.

As it was clear last night your thread inspired me to have a go at this subject as well, but mine is MUCH noisier.

Carole

[The Thing]

That re-process looks much better Duncan, where has all the noise gone.

These are the original process where the amp glow wasn't removed by the darks.

[The Thing]

Thanks for all the previous comments. This is reprocessed version with final tweaks to colour, levels, blur/sharpen in PhotoFiltre which seems very happy to process 16bit TIFs unlike GIMP. I have reduced the dark multiplication factor to 2.0000 and used a basic median stack (in DSS).

I think this may be my best image yet.  

Full size

[MarkS]

It's looking much better already - it's a good start to the processing.  

Now here are 3 definite steps to improve this further:
1) I think the dark multiplication factor is still too high - leading to a black ring instead of amp glow and some dark streaking.  Try reducing it further to see what happens.
2) The vignetting needs to be corrected - see how it gets darker towards the corners.  If it's too late to shoot some flats then some kind of gradient removal might do the trick.
3) There is too much green in the background and in the Flaming Star.  If that green can be subtracted then the red H-alpha will look much redder and the blue nebulosity will look much bluer.

Hope that helps,

Mark

[Later Edit]
It would give a result something like this:



One final tip:

I sometimes find that the amount of dark subtraction required to minimise the streaking is different to the amount of dark subtraction required to minimise the amp glow.  In such a case, I process twice and judiciously combine the two images to get the best of both.

[The Thing]

Thanks Mark.

Vignetting: I have used flats but DSS doesn't seem to take much account of them. All other images I have processed in DSS have shown the same issue.
Darks: I think I'm flogging a dead horse with DSS, I am going to reprocess in IRIS and see what I get.
Colour: I'm hopeless at gauging colour casts so all comments gratefully received!

[The Thing]

This image has had a few pixels trimmed off the edges.
Everything else is the same. Final tweaking in Photo Filtre. I think IRIS is worth the effort.

Full Size Version.

[MarkS]

So much better Duncan!

It's instantly obvious from the lack of background noise and background streaking that the darks have been subtracted properly now.  It makes so much difference.

I agree, IRIS is definitely worth the effort.

Well done.

Mark

[The Thing]

Thanks Mark.

[Fay]

Marks comments are always so helpful, he is honest & constructive, & everyone turns out to be a happier bunny than when they started     

[RobertM]

That's quite a massive difference from the first version.  You've done a very good job on processing and teasing out more of that elusive Ha but I think it would show even better if the black level was moved up a bit to give more contrast.  The background looks quite noise free now and I think the image could take it.  

Fay, I think we all try to be like that in our own way !

Robert

[Fay]

everyone certainly does Robert, & it is so helpful