Celestial hemisphere:  Southern  ·  Constellation: Sculptor (Scl)  ·  Contains:  NGC 253  ·  Sculptor Filament  ·  Sculptor galaxy  ·  Silver Coin
Getting plate-solving status, please wait...
NGC 253, Niall MacNeill
Powered byPixInsight

NGC 253

Getting plate-solving status, please wait...
NGC 253, Niall MacNeill
Powered byPixInsight

NGC 253

Equipment

Loading...

Acquisition details

Loading...

Description

This is I think my best deep sky image. It has been some time in the making. Even though there are undoubtedly improvements to be made as always, I am very pleased with this progress on my dso journey. I would value feedback from the many experts on this site who know much more of this area than I do and will see the imperfections and areas for improvement.

I captured data for this object from 2020-09-12 to 2020-10-14, so the final processing has been some time in the completion. Part of the slowness is that there is so much to learn and frankly so many mistakes to make. I took a break from it at times as well. :-D

In terms of the acquisition, I am grateful to the advice from John Hayes and Barry Wilson to take advantage of the 100,000 e- well depth of the SBIG16803 and increase my exposure times from 3 mins to 10 mins for LRGB and from 20 mins to 30 mins for Ha. I took this advice part way through the captures so I captured data with both exposure times. However, there was not a great deal of difficulty integrating the two even across one colour channel.

I captured the following:

Reds 66 x 3mins

Greens 96 x 3mins

Blues 34 x 3mins & 12 x 10 mins

Ha 6 x 20 mins and 17 x 30 mins

Total Integration Time: 22.3 hours....probably too much for Bortle 2 skies

In terms of calibration images:

Bias: 35

Darks: 35

Flats: 35 per colour channel......with swapping to planetary in between there were however multiple sets.

After some discussions I ended up integrating the Ha with RGB at the linear stage. Clearly opinion is divided on this and both can work, but as I understand it colour is easier to manage at the linear stage. That is not to say the there aren't many accomplished practitioners who do it perfectly well at the non-linear stage. Careful preparation of the Ha Master was necessary to eliminate gradients and noise which would otherwise come through the integration step.

I made a super Luminance from the LRGB and Ha data. In some ways I was disappointed with what it added to the HaRGB image and this may be because I captured quite a few hours of data for these. From here I need to ascertain whether to just capture RGB and Ha and then go with a Synthetic Luminance or perhaps , cut back on RGB, even binning and go longer with Luminance.

Rodney Watters was a huge help to me in that he processed the raw data and he gave me some key leads and advice along the way, including coming up the PI learning curve. I take my hat off to his skills.

Of course many of you are very familiar with this marvellous galaxy. It is large (27.5' x 6.8') being only 11.4 million l.y. away. With a Declination of −25° 17′ 18″, it is very favourably positioned for southern hemisphere astro-imagers and it is nice to pick big easier targets when you are starting out. It is just smaller than the Milky Way with a diameter of 90,000 l.y.

The Ha signal was so much stronger than for my last target NGC 6744 and it was a pleasure to work with this stronger signal.

As for colour and saturation, I have chosen this level and I hope it is within the expectation envelope for a galaxy such as this. Every version of this galaxy I have seen on AstroBin or the internet is so different you would hardly believe we are imaging the same galaxy, so I can only conclude the there is much subjectivity in the final colour rendition.

Comments

Revisions

  • NGC 253, Niall MacNeill
    Original
  • NGC 253, Niall MacNeill
    B
  • NGC 253, Niall MacNeill
    C
  • Final
    NGC 253, Niall MacNeill
    D

B

Description: Based on some feedback, the blue in the spiral arms from hot, young stars was muted and I adjusted the histogram to bring it up. My thanks to those who gave me this advice. I feel this is much closer to the mark.

Uploaded: ...

C

Description: Ha image

Uploaded: ...

D

Title: NGC 253 reworked

Description: The benefit of cloudy skies, is the time to go back and relook at data/ images that you've been wanting to do for a while. NGC 253 was my second deep sky image taken with my C14 EdgeHD and the SBIG 16803. Finally I had overcome the myriad of technical issues I had run into. 
However, having overcome the "engineering" issues, I then set about processing the data, without the benefit of much dso image processing experience. I think I did a fair job, given that but I was never rally happy with it.
Previously I integrated the Ha and RGB at the linear stage and I had to do a lot of work with masks etc to avoid noise from the Ha image giving the background a horrible red hue. These days I do it at the non-linear stage and that is far easier and creates a minimum of problems. Getting the stretch on the Ha image right before integration is very important and I made a number of iterations on that. 
As I processed this, the blue colour of the spiral arms and the yellow/ gold colour at the galaxy's centre came through beautifully. I had lost the blue or taken it down too much in the original version. There is a great deal of subjectivity on the intensity of a galaxy's colour in an astro-image, but I think the consensus seems to sit with a deeper, more intense colour saturation image and I think this is closer to that mark. I hope you agree. It certainly makes the image, at least to my eye, more aesthetically pleasing.
I chose this orientation as it is easier on the brain.
​​​​​​​

Uploaded: ...

Sky plot

Sky plot

Histogram

NGC 253, Niall MacNeill