Cone nebula

[cfpendock]

This is the Cone nebula in 7nm Ha.  It is a bit noisy probably because it need more time, but the weather is making imaging time severely limited at the moment…..  

 

The image is made from 5 x 20 and 12 x 15 minutes, i.e. 4 hrs and 40 minutes total.  Tak and Atik as in sig.  Stacked in DSS, processed in PS. 

 

I think there is more detail to be brought out of the nebulosity, and possibly there are too many stars?  But (as for  some other images), I like this one in Ha.

 

Any comments or criticisms would most welcome.

 

Chris

 

 

[carastro]

Really like that.

Carole

[swag72]

Love this Chris - Well processed and great data

[laudropb]

Smashing image, full of interesting detail.

[gorann]

I cannot think of a better way to spend 4 h and 40 min. I think it is superb in all its detail!

[cfpendock]

Thank you very much Carole, Sara, Laudrobp, and Gorann.  

 

I have to admit that when I first posted the image I was disappointed by the uploaded reproduction.  It was only after I clicked on the image and saw the “Full Size” button that the quality improved dramatically.  What a nice surprise!  Normally, because of my incredibly low internet speed, I don’t do this - it is bad enough now just trying to open the SGL pages!

 

The reason for the two different length of subs (20 and 15 minutes) was that I wanted to see if there was any discernible difference in image quality.  I have to say that I couldn’t see any difference in the initially stretched images.  However, it seems to me that if it is necessary to do any extreme stretching, then assuming that there are no areas which are fully saturated (excluding stars which can be dealt with separately), the longer subs should be able to take more stretching before posterisation, simply because the initial unstretched image will be spread over a wider range of brightness values.   

 

Any comment????

 

Chris

[Scott]

love it Chris. and well done on getting 4.40 hrs of imaging ;). I had a crack at this with the 414ex just before christmas and didn't come out half as well as this so kudos to you.

right or wrong, I'm trying to get more short (15min) subs than say half as many 30min. this is based in a solid understanding of the "suck it and see" methodology.

actually it's because I like to get at least 12 subs per channel and its more likely with 15 min subs and if weather permits after this, I'll go for more

 

[cfpendock]

Thank you very much Scott.  Yes, it's clear to me that I will need to do a lot more experimenting with shorter subs - normally for Ha I like to get around 18 at 20 minutes each. This seems to yield the smoothest results, but would 24 at 15 minutes be different?  Certainly while imaging "between clouds" it might make things easier....

Chris

[Scott]

Seriously Chris, I have no idea. I guess from a nice dark site the longer subs would pick up more of the finer stuff but from my somewhat light polluted garden, I'm not sure going longer would be of any help. I guess there's not a huge difference between 15 and 20 mins anyway

I often think how lucky our members in France or Spain are that they get enough clear skies to experiment. Here, even if you did take your time and test things over a period of time,  our skies are so prone to seeing variations that its impossible to tell what has caused the improvement/degredation

I'd say whatever you are doing, keep it up, coz it's working

[MartinB]

That's a beauty.  Very nicely processed.

With narrow band images you need very long exposures  for sky glow to rise above the read noise even in light polluted areas.  The longer you can go the better (unlike broad band imaging) however it is a compromise.  If you go too long you can't get enough subs for a decent sigma reject and also it makes you weep if the clouds roll in 1 minute before the end of a long sub!

[Martin-Devon]

Chris, that's a very fine Cone nebula. In terms of picking up the faint stuff and exposure times, as others have suggested, it's likely a compromise under UK skies. If you can get regular uninterrupted long clear runs then go for 20 minutes (assuming your guiding is excellent). For the last couple of months I've tried this under Devon skies and struggled somewhat, mainly because despite the weather forecast usually pesky clouds still drift in/out during the course of some 20 min imaging runs (star faded is the warning sign on the guiding) and I've lost a lot of subs due to this. Maybe you have better skies, if so try to go for the long subs.

Martin 

[ollypenrice]

You say its noisy but be fair to yourself: it's very deep indeed. Lovely stuff.

Olly

[astro mick]

Very nice image indeed.Looks quite smooth to me.

Mick.

[cfpendock]

On 13 February 2016 at 10:51, Scott said:

I often think how lucky our members in France or Spain are that they get enough clear skies to experiment.

Me too.....

19 hours ago, MartinB said:

If you go too long you can't get enough subs for a decent sigma reject and also it makes you weep if the clouds roll in 1 minute before the end of a long sub!

 

4 hours ago, Martin-Devon said:

despite the weather forecast usually pesky clouds still drift in/out during the course of some 20 min imaging runs

Precisely.  But unfortunately I still think that extreme stretching for faint stuff needs the longer subs.

 

Thank you very much to you three above, and also Olly and Mick for your kind comments.

I might try dithering at the next opportunity to see what difference that can make.....

Chris

[Barry-Wilson]

This is a very good image Chris and very well framed.  With the weather we've had over the last few months, this is agreat image, one to be very pleased with.  There are options for boosting contrast and star reduction, but it is so easy to over process an image one tiny iteration at a time.

I have opted for 20min NB subs latterly in place of 30min for the reasons listed - cloud dodging and numbers for sigma rejection as an overall optimum balance.

[gorann]

When I saw the fine detail in your Ha image I started again thinking about running a dual rig with one scope taking Ha (with my Atik 460) and the other collecting colour (with my Canon 60Da).

So I could not stop myself from doing a test. I shot the Cone Nebula about a week ago with the DSLR and the colours were ok but the detail was nowhere near that of your Ha. So, I took the liberty of borrowing your Ha data to see how it would work, and here is the result. I used 75 % of you Ha and 25 % of a b/w version of my image to produce the luminosity layer. Then I blurred my colour image and removed most of the stars before I added the luminosity.

Most of the work was to rotate and scale the images to make them line up. I did that in Photoshop but I expect there are some better way to do it in some other program. There are some issues with the stars but on the whole it seems to work out.

My original colour image is not much to show, it was also a hazy night, but I add it to the post here anyhow to show how much difference the Ha data did for the detail.

I really hope you do not mind - it was just to see if I could pull it off.

[cfpendock]

Goran - of course I don't mind you using my image - in fact I feel privileged!  After all, this is the world wide web on which I have chosen to "broadcast" my image - to anybody....

As for the result.  Well, in my view some objects lend themselves to colour, and others are better rendered in mono.  This is one.  Another is the elephant trunk nebula.

I think that in any case, for me the combination image is too red, but you are right: the Ha has certainly given more detail.  It is interesting that it has also produced/enhanced some halos around the stars.  I know in the Ha version there was a faint halo around the star in the centre, but I thought that this was due to fairly extreme stretching.  I think the combined image would be improved by reducing the saturation in the nebula, but seriously increasing the star colour.

Chris

[Guest]

Excellent work - I'm thinking of ditching my one shot colour camera and going mono/ha - looks like fun :-)

[gorann]

I guess I am a junkie for colour, but I see you point. Do you think this is a bit better?

[cfpendock]

Nope.  Well, yes, I find your second attempt marginally less "in your face", but I still prefer this one in mono.  But good on you for trying!  

Sorry Goran.

chris

[gorann]

My exercise was really only to see how demanding it would be to do the processing from a dual rig with Ha on a CCD and RGB on a DSLR. Then, there are so many ways to process an image and an indefinite numbers of outcomes. I am mainly not very pleased with what the stars look like. If you generally prefer B/W over colour on this object then I can see you point and respect that but Ha is a red wavelength so if our eyes were as sensitive as a CCD camera at long exposures, this object would at least be red. 656 nm light looks like this:

[gorann]

Oops, did not mean to make that red square as big - that is really in your face. Sorry.

[Guest]

32 minutes ago, gorann said:

Oops, did not mean to make that red square as big - that is really in your face. Sorry.

That was hilarious Gorann - thanks - made me laugh on a miserable/busy Tuesday! :-)

So glad you got in there with the second post before your forum friends "released the hounds" LOLOL

David