NGC6888

[alan4908]

For this bi-colour image of the Crescent Nebula I mapped Ha to red, OIII to blue and created a narrowband synthetic green. I acquired a few broadband subs for the LRGB starfield but also decided to create a broadband synthetic green.  Since the Ha signal is dominant, I gave the OIII signal quite a long exposure. The total acquisition time was 14.5 hours.  

Wide field:

 

Crop:

LIGHTS: L:5;R:7;B:12 x 600s; Ha:5; OIII: 16 x 1800s. BIAS: 100; DARKS: 30; FLATS: 40 all at -20C. 

Alan

[laudropb]

Very nice capture.

[wimvb]

I like the way the Oxygen envelopes the Hydrogen in this nebula. Well captured. Am I correct in guessing that this will be continued?

[alan4908]

Thanks for the comments. 

9 minutes ago, wimvb said:

I like the way the Oxygen envelopes the Hydrogen in this nebula. Well captured. Am I correct in guessing that this will be continued?

Wim - having done a bit of research into the generation of synthetic green (narrowband and broadband), I'm not sure that there is much to be gained from capturing SII. It is quite surprising how well this seems to work (I used Noel Carboni's actions). 

My original intention was to do a Hubble Palette, however,  after I acquired  a few hours of SII and discovered it was really faint, I changed strategy and went for a bi-colour !

[johnrt]

Very nice indeed, you have the OIII shell there clear as day!

[alan4908]

10 minutes ago, johnrt said:

Very nice indeed, you have the OIII shell there clear as day!

Thanks John - yes, I was very pleased with the OIII contribution, I did give it 8 hours on this filter since I was trying to get it to be approximately the same strength as the Ha signal.

Alan

[Benno]

Very nice image

[PhotoGav]

Excellent result and a very well defined OIII shell.

My only criticism would be that, to my eyes, the stars look slightly blurred or maybe elongated, especially more towards the top of the frame. It doesn't really distract from the whole image, but the reason I mention it is that I wonder if there is a focus, guiding, PA or spacing issue at play here? If the stars were sharper, then the target itself would surely benefit too. Just a thought...

How do you find the 3nm Astrodon filters? I have Astrodons on my wish list, but am not sure if 3 or 5 nm is best with our southern UK skies? You certainly make the 3nm look very usable!

[alan4908]

Gav

Thanks for the comments.

9 hours ago, PhotoGav said:

My only criticism would be that, to my eyes, the stars look slightly blurred or maybe elongated, especially more towards the top of the frame. It doesn't really distract from the whole image, but the reason I mention it is that I wonder if there is a focus, guiding, PA or spacing issue at play here? If the stars were sharper, then the target itself would surely benefit too. Just a thought...

How do you find the 3nm Astrodon filters? I have Astrodons on my wish list, but am not sure if 3 or 5 nm is best with our southern UK skies? You certainly make the 3nm look very usable!

I agree with your star field point - I believe it's field curvature that seems inherent in my scope but I may be incorrect. I've noticed this on all of my images and it's something that I normally minimize in post processing - this time I didn't, since there seemed to be too many stars at the edge with defects . This is one of the aspects (the other being chromatic aberration) that is driving me in the direction of looking for a scope upgrade. Do you find similar issues with your SW Evostar ?

On your question about the Astrodon filters. Yes, I'm very happy with them. I decided to go for the 3nm variants simply because I had read that they maximized image contrast over the 5nm option, the other factor was that I was interested in minimising light pollution from the moon since I image DSO's when the moon is up. Here, I instruct ACP to follow the Lorentzian algorithm, so that my scope only acquires images when the moon is greater than a certain angular distance from the object.  This "moon avoid" approach appears particularly effective with the 3nm filter variant.    

Alan

[PhotoGav]

Thank you, that's interesting about the 3nm. I am now back to favouring them again!

I haven't found major issues with stars using my SW ED80, in fact it's a great little scope, especially for the price. Having said that, I did have issues at one point, but I soon worked out that the spacing was slightly wrong. I had an extra spacer that was not required. Once removed, edge to edge near perfection! You might just check that you have the correct spacing from reducer to chip. If it were PA the stars would show radial elongation, which I don't think is the case here. I would hope that your mount is nigh on perfect for PA anyway in your lovely IKI ROR obsy! I think that a single sub would help to identify the problem as you have done too good a job in the processing!

As an aside, I am in the process of planning an obsy and will most likely go for the Rigel pier. Would you please do me a favour and tell me what the diameter of the base is - just for my planning purposes!

[DaveS]

If you already have the 3nm HII filter, then it could be worth adding the 3nm [NII] one as well. Some targets are quite rich in [NII], a lot more than [SII]. Might be worth looking at this in [NII] instead of [SII].

That gaudy multi-coloured blob in my avatar is the Rosette in [NII], HII, [OIII].

 

BTW Gav, the base of the Rigel Pier is 450mm, I have one myself.

 

Edit: Not sure of dia now, will measure when I get home.

[alan4908]

1 hour ago, PhotoGav said:

Thank you, that's interesting about the 3nm. I am now back to favouring them again!

I haven't found major issues with stars using my SW ED80, in fact it's a great little scope, especially for the price. Having said that, I did have issues at one point, but I soon worked out that the spacing was slightly wrong. I had an extra spacer that was not required. Once removed, edge to edge near perfection! You might just check that you have the correct spacing from reducer to chip. If it were PA the stars would show radial elongation, which I don't think is the case here. I would hope that your mount is nigh on perfect for PA anyway in your lovely IKI ROR obsy! I think that a single sub would help to identify the problem as you have done too good a job in the processing!

As an aside, I am in the process of planning an obsy and will most likely go for the Rigel pier. Would you please do me a favour and tell me what the diameter of the base is - just for my planning purposes!

Hi Gav

Welll, it's good to know that you don't have similar issues with your SW ED80. Maybe I'll try varying the distance,  however I'll first need to acquire either a variable spacer or additional spacers. I'll also have a look at the original subs to see if I can see anything suspicious.  Overall, I do really like my ED80 which is why I haven't taken the upgrade path yet. 

On the subject of the Rigel Pier yes - I like it,  mainly because of the "fins".  Since these are flat I attached some black D-line ducting within which I route the various cables which makes everything quite tidy - have a look at gallery for some pics of my obsy. 

On the subject of the Pier diameter, I can only give you a very approximate estimate of 60cm since the base is partially hidden by my shock resistant flooring (which I decided to glue down after reading that it had a tenancy to expand with heat).  I'm sure if you gave Pulsar Observatory's a call they could give you the exact dimensions.  

Alan

[alan4908]

7 minutes ago, DaveS said:

If you already have the 3nm HII filter, then it could be worth adding the 3nm [NII] one as well. Some targets are quite rich in [NII], a lot more than [SII]. Might be worth looking at this in [NII] instead of [SII].

That gaudy multi-coloured blob in my avatar is the Rosette in [NII], HII, [OIII].

 DaveS 

That's interesting I may well do that.  As an aside, what reference source do you use in order to determine which narrow filters would give the optimum results for a particular object ?

Alan

[DaveS]

Hah, the only reference source is "suck it and see"!

Supernova remnants are usually rich in nitrogen, as are some molecular clouds. All I do is take a reasonable sub at 4x4 binning, say a minute or so (= 16 min at 1x1) and see what shows up on the screen. For instance, the Rosette is almost as strong in [NII] as HII.

M27 is worth a look in [NII], see Astrodon site.

Having four NB files gives you several options for tricolour mapping, eg looking at just the red wavelengths HII, [NII], [SII], or perhaps leaving out the overwhelming HII and just looking at the forbidden lines of [SII], [NII] and [OIII].

[PhotoGav]

Thank you for the pier info Alan & Dave. 

Interesting discussion about NII in targets. Definitely one to consider. Every step of this journey makes me realise what a huge and varied field it is. Wonderful!

[DaveS]

I've just checked my pier. The base *is* 45cm dia, and the holes look to be on 28cm centres.

HTH

Dave.

[PhotoGav]

1 minute ago, DaveS said:

I've just checked my pier. The base *is* 45cm dia, and the holes look to be on 28cm centres.

HTH

Dave.

Perfect, thank you!

[ultranova]

Wow what a outer shell, I don't think I have seen such a prominent outer shell,

Looks like all that imaging time as paid off, very nice indeed,

My only small criticism is it looks a little over processed,

I think backing off a tad will reveal more detail.

well done

Paul 

[alan4908]

26 minutes ago, ultranova said:

Wow what a outer shell, I don't think I have seen such a prominent outer shell,

Looks like all that imaging time as paid off, very nice indeed,

My only small criticism is it looks a little over processed,

I think backing off a tad will reveal more detail.

well done

Paul 

Thanks Paul  

Yes, I was very pleased with the outer shell, not so pleased with the starfield.  On the over processing point,  I find it more difficult on these tone mapped images to know when to stop. I was attempting to create a realistic looking image but I guess this is largely subjective. Do you have any tips on what processing aspects you would lower to reveal more detail ?

Alan

[ultranova]

6 hours ago, alan4908 said:

Thanks Paul  

Yes, I was very pleased with the outer shell, not so pleased with the starfield.  On the over processing point,  I find it more difficult on these tone mapped images to know when to stop. I was attempting to create a realistic looking image but I guess this is largely subjective. Do you have any tips on what processing aspects you would lower to reveal more detail ?

Alan

Hi Alan, I don't use the software you do so I can not give much advice I am afraid, I mainly use pix insight for main work flow with

a little tweaking in PS elements,

if your using some sort of smoothing process to cut down on the noise, which I use in PI it can be easy to over do it a tad

and also slightly over stretch the image to reveal more detail, I think quite a few of us a guilty on that front,

colours  are great , but to me on my screen The background especially looks a bit to soft, again as you say, it is subjective

and another persons likes is another persons dislikes.

overall though a great image and I love that out shell

Paul 

 

[cloudbuster]

very nice.....with the outer shell coming thru nicely!

[alan4908]

2 minutes ago, ultranova said:

Hi Alan, I don't use the software you do so I can not give much advice I am afraid, I mainly use pix insight for main work flow with

a little tweaking in PS elements,

if your using some sort of smoothing process to cut down on the noise, which I use in PI it can be easy to over do it a tad

and also slightly over stretch the image to reveal more detail, I think quite a few of us a guilty on that front,

colours  are great , but to me on my screen The background especially looks a bit to soft, again as you say, it is subjective

and another persons likes is another persons dislikes.

overall though a great image and I love that out shell

Paul

Paul - thanks for the feedback - there is definitely noise reduction in there, basically because the dark areas where a bit noisy .  Anyway, if I every reprocess this image, I'll have look at the noise suppression levels a bit more closely. I'm also using Pixinsight but I'm only at the early stages. So, far I've found that it does a much better job at gradient elimination (eg DBE) compared to the PS equivalent.  I'm currently experimenting with the other functions and comparing them to PS equivalents, so if there's another PI function that you think is much better than the PS equivalent, please let me know. 

Alan

 

[ultranova]

Hi Alan, a good one to try if you haven't already is TGVdenoise,

which is in the noise reduction category, I find the stock setting a little high

its a great one to experiment with  , and combining that with range selection to make a mask

so you turn TGVdenoise up a bit to smooth out the background , without damaging the highlights

its a bit like selective layer masking.

I think there are tutorials on this some where but I cant remember where I saw it,

Paul

 

[wimvb]

Noise reduction in PI is an art and can sometimes be difficult to get right. I have found that sometimes you can get a more pleasing result if some noise is left in the image. When doing Multiscale Transforms, the amount can be set lower than 1 to leave a little noise. For TGVDenoise I sometimes use a 0.5 gray mask to leave some noise. This also makes blobs that can be left over from noise reduction of DSLR images, less prominent. For the last few images I have processed with PI, I have not used any noise reduction at all, except for SCNR to get rid of excessive green. A careful CurvesTransformation could handle the noise in those images. This was for relatively bright objects.

For an object such as the crescent with its faint details, you'd definitely would need to spend time to get it right.

[wimvb]

You may have a look at this thread on the PI forum:

http://pixinsight.com/forum/index.php?topic=8942.0