M31 Andromeda processing in DSS - advice please

[Fordos Moon]

Spent the last couple of nights battling against mist and ligh polluion but wanted to practice imaging so managed 27x 120 secs of M31 at ISO 400. Got darks too and processed using DSS.

The first pic is a single capture in DSS having experimented with RGB levels, luminance and saturation (following various guidance in DSS) and levels and curves in PS.

The 2nd is 19 stacked (albeit getting misty) and DSS RGB, luminance and saturation only.

The 3rd is as the 2nd, slightly toyed with in PS.

I've noticed two black blemishes so I know to check and clean lenses but what else can you advise other than more captures and less moon soaked misty nights?! eg have i over-exposed?

ps I have a feeling I might have double processed one or more of these in the DSS RGB, lum. sat stage...any help appreciated

[Fordos Moon]

Of particular concern in last 2 images is a thin white line from top right to centre left at 90 degrees to the galaxy when looked at closely.

Is this processing or something out there?!!

[cp255]

You can take flats to remove the dark blotches. Also remember to take darks flats, bias, and darks as well. Also I notice a streak through your image. That can be fixed by using something other than an average since the outlier will be removed. Try stacking with median or kappa sigma clipping.

[ollypenrice]

cp255 is right that you need darks to calibrate your flats but these don't need to be dedicated darks. A master bias will do perfectly well as a 'dark for flats' and this will save an enormous amount of time. Flats, though, are very important indeed, especially if you are battling with gradients as you will in LP.

You haven't over exposed. Teasing detail out of the core of M31 is very difficult and needs some fairly advanced post-processing techniques.

This image could be further flattened in post processing to remove the central green-magenta gradient. If you have Ps then the plug-in Gradient Xterminator by Russ Croman is good. The best tool of all is Dynamic Background Extraction in Pixinsight. Another useful weapon, free/donation, is Hasta La Vista green on the Deep Sky Colors wesite. This gets rid of unwanted green noise and is very useful.

Olly

http://ollypenrice.s...39556&k=FGgG233

[Fordos Moon]

Many thanks chaps. I'm encouraged to know I have at least not overexposed and as a beginner I am relatively chuffed with this start point.

Conditions were poor. I am considering getting one of the filters from FLO for this set up to help with LP.

[Fordos Moon]

Chaps what proportion of lights do I take for flats and bias frames?

[ollypenrice]

Flats need to be sufficiently numerous to have little reisdual noise. Opinion varies but I take about thirty, usually. Bias are so quick to take that I run off about fifty. I can't see why the number of darks, flats or bias should be related to the number of lights. I'm prepared to be enlightened, though. For me the idea is to get the noise down in all of them, so the more the merrier.

Olly

[Fordos Moon]

Thanks Olly, it was only that the number of darks relates to lights so I assumed the others might.

[ollypenrice]

Thanks Olly, it was only that the number of darks relates to lights so I assumed the others might.

I don't believe it does, though. Where does this idea come from and what's the theory behind it?

Olly

[Fordos Moon]

I may have dreamt it! Ps my flats are coming out blue like the sky a bit does this matter or should I increase thickness of white tee shirt?!

[Fordos Moon]

Ps you may have guessed I am an amateur, but enthusiastic!

[Fordos Moon]

I could swear. Went outside and shot flats but forgot to switch camera to AV :-(

[Cloudwatcher]

I'm not an imager I'm afraid so can't advise on flats,darks etc. but I think the image can be improved further in Photoshop. The 'white line' can be removed for the most part using the Healing Brush. Play with the colour balance and reducing the saturation will help to show more detail which can then be brought out with the Dodge and Burn tools.

I also think M31 looks better 'the other way up'.........Don't know why ............Anyway here's my lunchtime effort.

[Fordos Moon]

Wow that does look good! Was that with my image?! You must know that you are doing with photoshop, thanks for the saturation advice too!

And it does look better that way up!