M33 in HaRGB

[wimvb]

My take on this galaxy. One of my first imaging sessions this season, and from my new home under considerably darker skies than before (Mag 20.6 vs 18.5).

Gear: SW 150PDS on a SW AZ EQ6 and ASI174MM cooled cmos at 2 e/ADU.

• Ha: 14 x 5 minutes
• R: 24 x 3 minutes
• G: 20 x 3 minutes
• B: 19 x 3 minutes

(Total: 4 hours and 19 minutes)

Capture: Ekos/Kstars

Processing: PixInsight

I had a planned sequence in Ekos for exactly one hour each of Ha, R, G and B. But just before the last blue sub, Ekos decided it was time for an automated meridian flip, which it did without hickup. I decided to let it run for half an hour more, collecting Ha and R. This image is about the full fov of my camera, only the edges have been cleaned up.

(click on the image to enlarge)

[tooth_dr]

Nice job Wim.  Surprising what you can capture from a darker site for short exposures!  

[wimvb]

Thank you. Yes, I was pleasantly surprised.

[peter shah]

This is lovely. Rich colour with those HII regions standing out nicely

[gorann]

Really great to see that you finally are up and running after moving out of town. I think I can see in your image how dark the new sky is. Very nice colours and details. Congratulations!

[Hallingskies]

Nicely processed, with subtle colours.  Some folk are tempted to overcook this one but I think you have it just right.

[wimvb]

2 hours ago, peter shah said:

This is lovely. Rich colour with those HII regions standing out nicely

Thanks Peter. Your masterpiece was an inspiration. But a comparison also shows that I still have a lot to learn / finetune in my setup. Apart from the obvious fact that a SW 150PDS/ASI174 is no match for an AG12/H35. ?

Just as in your image, the colour comes with just using RGB. In my experience, as soon as I go for contrast in a luminance master, and combine LRGB, it tends to wash out the colour. If I extract L from an RGB image, the contrast is generally much lower than in the luminance master, which is quite obvious from colour theory of course. Imo, when the detail is present in RGB, there's no use in adding L to an image.

[wimvb]

1 hour ago, gorann said:

Really great to see that you finally are up and running after moving out of town. I think I can see in your image how dark the new sky is. Very nice colours and details. Congratulations!

Thanks Göran. Dark skies really make all the difference. On a claer night I can just about see the Andromeda galaxy with the naked eye. Unfortunately those clear skies are just as few as from Stockholm.

[wimvb]

1 hour ago, Hallingskies said:

Nicely processed, with subtle colours.  Some folk are tempted to overcook this one but I think you have it just right.

Thanks. I try to hit that Goldilocks zone in processing, but it's generally not an easy target.

[peter shah]

34 minutes ago, wimvb said:

In my experience, as soon as I go for contrast in a luminance master, and combine LRGB, it tends to wash out the colour. 

Adding luminance will allow you to give a more aggressive noise reduction to the colour layer without damaging your detail. It is important to match your luminance stretches with the RGB or the colour will suffer. You can push the RGB stretch futher but this will introduce colour noise. If you apply too much of a noise reduction it will show as blotchy colour. So there is a fine balance.  The answer is really more RGB subs. You can increase the signal in the RGB by binning 2x2 if you wanted. I don't do this I just get more frames and bin everything 1x1

[tooth_dr]

So much to learn. It’s great that forum members are so generous in sharing their experiences 

[wimvb]

2 minutes ago, peter shah said:

You can increase the signal in the RGB by binning 2x2 if you wanted. I don't do this I just get more frames and bin everything 1x1

My camera is CMOS, so binning doesn't improve snr as much as it does with ccd.

4 minutes ago, peter shah said:

It is important to match your luminance stretches with the RGB or the colour will suffer.

That's my experience also.

5 minutes ago, peter shah said:

Adding luminance will allow you to give a more aggressive noise reduction to the colour layer without damaging your detail.

Moving to a dark site has proven the best noise reduction I could hope for. From my previous (suburbian) location with a street lamp just in front of my garden, I would need to use heavy noise reduction. Now I just did a very mild reduction at the end of the workflow.

[toxic]

thats nice - deep and moody colour 

 

[wimvb]

1 hour ago, toxic said:

thats nice - deep and moody colour 

 

Thanks Chris.

[Petergoodhew]

That's an impressive M33 Wim - I do like the subtle use of colour.  It's a personal thing, but I really dislike heavy levels of saturation that make images look more psychedelic than natural.

As I consider myself a beginner I'm reluctant to offer opinions and advice to anyone, but lately I've been experimenting by combining L,R,G, and B all together to create a super luminance. My thinking is that the sky background is where the noise is greatest (given that the signal to noise ratio is lowest) and so by creating a super luminance I'm getting to use all of the data to minimise the noise level.  With enough subs, and a dark sky, I find I no longer need to do any noise reduction in processing.

[wimvb]

Thanks Peter. Yes, a dark sky makes all the difference. I somtimes use a synthetic luminance, but I wonder if it will make much difference here. Something to experiment with on cloudy nights, I guess.