NGC7331

[alan4908]

The galaxy NGC7331 is located in Pegasus and is approximately 46 million light years distant. It's estimated to be be substantially larger than our own Milky Way with a transverse diameter of 140 000 light years.   Some background galaxies can also be seen in the image (below), which are estimated to be c300 million light years distant  Due to its high inclination of 77 degrees, part of the disc is blocked by dust lanes, although I was quite pleased with the amount of detail captured. 

The LRGB image represents 11.5 hours integration time and was taken with my Esprit 150.

Alan

LIGHTS: L: 16, R:17, G:17, B:19 x 600s. DARKS:30, FLATS:40, BIAS:100 all at -20C.

[Davey-T]

Very nice Alan, been taking subs of it on and off on recent clear nights, hope mine comes out anywhere as good as your version.

Dave

[peter shah]

A great shot with lovely colour and scale to it

[alan4908]

5 hours ago, Davey-T said:

Very nice Alan, been taking subs of it on and off on recent clear nights, hope mine comes out anywhere as good as your version.

Dave

Thanks Dave - it took me rather a long time to acquire this, which wasn't particularly helped by the UK weather...... Good luck on your own rendition !

1 hour ago, peter shah said:

A great shot with lovely colour and scale to it

Thanks Peter. 

[kirkster501]

Very nice.  I'm liking it very much.  A new one on me this object.

[tomato]

Great result, the Deer Lick cluster is nicely framed also.

I’m trying to be patient while construction of my permanent observatory continues, but having the 150 stuck in it’s case now the dark nights are back is frustrating to say the least.

[alan4908]

13 hours ago, kirkster501 said:

Very nice.  I'm liking it very much.  A new one on me this object.

Thanks for the comment. 

12 hours ago, tomato said:

Great result, the Deer Lick cluster is nicely framed also.

I’m trying to be patient while construction of my permanent observatory continues, but having the 150 stuck in it’s case now the dark nights are back is frustrating to say the least.

Thanks.

It must be very frustrating for you, still you should have a nice observatory to look forward to soon.

Alan

[StuartJPP]

A cracking image, love these galaxy shots.

[alan4908]

16 hours ago, StuartJPP said:

A cracking image, love these galaxy shots.

Thanks Stuart  

Alan

[dave_galera]

Beautiful image well captured

[ollypenrice]

Very nicely done indeed. Just a thought but for that very bright innermost little core have you considered using your RGB-only in the way that you'd use a set of short luminance subs just to stop that bit saturating?

Olly

[alan4908]

1 hour ago, dave_galera said:

Beautiful image well captured

Thanks Dave. 

14 minutes ago, ollypenrice said:

Very nicely done indeed. Just a thought but for that very bright innermost little core have you considered using your RGB-only in the way that you'd use a set of short luminance subs just to stop that bit saturating?

Olly

Thanks Olly. No I hadn't considered that but it is a good idea to try, so thanks for the tip.

It is a very interesting object to process due to the high dynamic range of both the galaxy and the surrounding stars, some of which are quite bright. 

Alan

[gorann]

Beautiful! I like it a lot for many reasons. I was aiming at the same target for the first light of my 14" Meade LX200R (ACF) about a week ago. Olly  @ollypenrice will like the comparison since he argues for the superiority of large refractors, and I can see that you have about the same level of resolution. So your Esprit 150 is obviously a great galaxy hunter (fortunately I am also an Esprit 150 owner). To the 14" SCT defence I could say that I only grabbed 5 hours and it seems to have picked up the faint stuff a bit better. But maybe you did not stretch the data as much as I did. The final 5-hour version of my image is at the end of this string:

 

 

[alan4908]

17 hours ago, gorann said:

Beautiful! I like it a lot for many reasons. I was aiming at the same target for the first light of my 14" Meade LX200R (ACF) about a week ago. Olly  @ollypenrice will like the comparison since he argues for the superiority of large refractors, and I can see that you have about the same level of resolution. So your Esprit 150 is obviously a great galaxy hunter (fortunately I am also an Esprit 150 owner). To the 14" SCT defence I could say that I only grabbed 5 hours and it seems to have picked up the faint stuff a bit better. But maybe you did not stretch the data as much as I did. The final 5-hour version of my image is at the end of this string:

 

Thanks for the comment gorann.

It is interesting to compare the image from my Esprit 150 with that of your 14" Meade LX200R.  Your image looks very nice by the way, particularly for only 5 hours integration time !

As you say, they do seem to give a similar level of detail - perhaps at one level that is not surprising since I'm at  0.7 arc seconds per pixel and you appear to be at 0.85.  From my particular site, I've previously concluded that there's likely to be little benefit from a higher resolution DSO imaging set up.

On the faint stuff - a possible explanation for less nebulosity in my image is that this  consists of two blended images: galaxies and a star field. I deliberately stretched the star field much less than the galaxies to obtain better star colours and much less star bloat.  Hopefully you cannot spot the join. 

Alan

[Xplode]

Very nice galaxy!

Color balanse seems a little off.
What i don't like is the black background, it makes it look a little "lifeless".

You have lost a lot of faint background galaxies and also the faint dust because of the dark background.

Here's an area very close to NGC7331 (upper right corner), lots of faint yellow background galaxies can be seen and also the faint dust.

[alan4908]

14 hours ago, Xplode said:

Very nice galaxy!

Color balanse seems a little off.
What i don't like is the black background, it makes it look a little "lifeless".

You have lost a lot of faint background galaxies and also the faint dust because of the dark background.

Here's an area very close to NGC7331 (upper right corner), lots of faint yellow background galaxies can be seen and also the faint dust.

Hi Ole

Many thanks for your comment. You raise a very interesting point regarding the background level.

To me, there are two complementary approaches to the processing of deep sky objects:

1) Stretch the background and the main object of interest at the same level.  The main advantage of  this approach is that it highlights details everywhere. The main disadvantage is that you can end up with bloated stars, white star cores and white clipped objects which can distract from the object of interest.  This distraction effect will increase the more that the image is cropped since the background details will get proportionally larger. 

2) Process the background separately from the object of interest.  This has the advantage that you can control the relative emphasis level of the object of interest, star bloat can be better controlled and white star cores along with white clipped objects can be avoided. This also allows you to significantly crop images to emphasize the central object of interest without enlarging distracting background detail. The main disadvantage is that you loose background level details.

I use both approaches, selecting the approach that is appropriate to what I'm trying to achieve. 

In the above image, I choose approach 2) and ended up with a background level of about 18 (0= black, 255 = white). This was primarily because I wanted to dim the stars and background to a level that I judged emphasized the object of interest  (eg NGC7331) to best effect.  However, if this was a much wider field of view, say NGC7331 including Stephan's quintet, then I would have used approach 1). 

To me, this is all very much personal taste with no right or wrong answers. 

Alan