NGC6888 The Crescent - First Attempt at Narrowband

[daemon]

Hi All, This is my first real attempt at narrowband imaging (apart from a couple of test exposures).

This is about 2.5 hours from last night (Ha, OIII, SII). Mainly 40 x 180" subs in Ha. Fully processed in PixInsight. SW150PDS - Baader MPCC - ASI1600MM on EQ6R-Pro. Guided with PHD2.

My main issue here is my Coma Corrector, which I am told may not be spaced correctly - any further advice on this gladly received! 

The stars in the corners (even when cropped) are really elongated - almost as if the CC was not in place. I really need to fix this!

However, I am sure there are many more issues so...…….Criticism and Comments welcome!

Clear Skies!

Steve

 

[daemon]

I tried a crop to reduce the coma, and also adjusted the colouring.....maybe too much.

[MarkAR]

Apart from the coma you have some really good detail.

Colour wise on the Crescent, it's the current bane of my life. Toning down the green definitely works, much better.

[ebdons]

Nice one! the cresent is a challenge to get the detail right, cc spacing looks off, but the oiii gas is very hard to get it to show, not sure about sii? keep posting your images. ton

[Chefgage]

9 hours ago, daemon said:

I tried a crop to reduce the coma, and also adjusted the colouring.....maybe too much.

Colour wise I think I prefere the cropped one. Both very nice though.

[steppenwolf]

Unfortunately, you are right about the coma corrector. Which one are you using? Normally you would expect the spacing from the mounting face at the rear of the corrector to the sensor itself to be 55.0mm +- 1mm.

With regard to the image itself, you have some great data with some good detail in the OIII regions which give the Crescent the appearance of a 'plasma' halo.

[MarkAR]

Looks like you need extra spacer between CC and camera.

[alacant]

16 hours ago, daemon said:

main issue here is my Coma Corrector, which I am told may not be spaced correctly

Hi

Lovely shot. I find colour by far the most difficult part of astro processing. 

The Baader MPCC needs 57.5 mm from the shoulder of the m48 thread on the corrector to the camera sensor. I suspect you have only 55mm.

FWIW, I found the t2 route a bodge. Get a proper 48mm adaptor and eiether a 3mm or 4mm m48 spacer. A low profile filter ring without the glass is fine.

Cheers and HTH

 

[ebdons]

Yes the 150pds is f5 so do you need another type of cc or maybe not one at all, as I have one fitted on my f3.9 but found fitting a cc on my f5 orion introduced  defects at the edges and not fitting a cc it looked better. see what other folks say on here I might be wrong. ton

[steppenwolf]

Doh! The type of CC was in your first post 👀

I used one of these to very good effect in my F4.8 Newtonian so you should be getting better results than currently.

[des anderson]

A cracking image and for a first attempt a big thumbs up from me Des

[daemon]

Thanks everyone for all your comments!! Really appreciated!! 

Yes, I certainly think the spacing is the issue - I was imaging without the CC early in the week and definitely had significant coma. I installed the CC for Wednesday's session but installed it straight after the EFW and plugged the assembly into the draw tube. No difference to coma.

So my imaging train was:-

ASI1600 - EFW - MPCC - drawtube  

--- so I will try:-

ASI1600 - EFW - Spacing adapter/s - MPCC - drawtube

Once the skies clear again I'll experiment and maybe I'll post a sub here to show the difference.

As for experimenting with the colours I may try again with this data and may try an HOO combination (this was SHO - Hubble). May try with some PixelMath tips for PI that I have learned about.

Thanks again all!

 

[steppenwolf]

3 hours ago, daemon said:

As for experimenting with the colours I may try again with this data and may try an HOO combination (this was SHO - Hubble). May try with some PixelMath tips for PI that I have learned about.

I am a great fan of HOO and I suspect that you will find it an interesting way to image. Your first (green) image colours are typical of those of 'original' Hubble palette images and many astronomers manipulate the colouring to produce what is generally termed the 'gold and turquoise' palette which many feel is more attractive. One of the great things about 'false colour' narrowband imaging is that anything goes, there is no correct way!

[daemon]

1 hour ago, steppenwolf said:

I am a great fan of HOO and I suspect that you will find it an interesting way to image. Your first (green) image colours are typical of those of 'original' Hubble palette images and many astronomers manipulate the colouring to produce what is generally termed the 'gold and turquoise' palette which many feel is more attractive. One of the great things about 'false colour' narrowband imaging is that anything goes, there is no correct way!

I agree Steve. I do think I will become a big fan of narrowband. I love the flexibility that you mention. Especially as I am colour blind! 😁

I have both your books by the way and I am a big fan! Always dipping into them!

Cheers,

Steve

[daemon]

7 hours ago, alacant said:

Hi

Lovely shot. I find colour by far the most difficult part of astro processing. 

The Baader MPCC needs 57.5 mm from the shoulder of the m48 thread on the corrector to the camera sensor. I suspect you have only 55mm.

FWIW, I found the t2 route a bodge. Get a proper 48mm adaptor and eiether a 3mm or 4mm m48 spacer. A low profile filter ring without the glass is fine.

Cheers and HTH

 

This is great info alacant!! Really helpful. Thanks for posting it! 🙂

 

[steppenwolf]

3 hours ago, daemon said:

Especially as I am colour blind! 😁

I have both your books by the way and I am a big fan! Always dipping into them!

Being colour blind could be an advantage with narrowband 🤣 Delighted that you are enjoying the books

[daemon]

Well, I tried to produce an HOO image with the data I had and to be honest it didn't really work this time. I tried various PixelMath adjustments in PI but it did not seem to make a lot of difference. So I just went back to my original SHO integration and tweaked the post processing a bit. I've probably sacrificed some of the more subtle data for contrast and a darker background, but hey ho. Not sure I can do better with this data.

Once I fix the Coma Corrector spacing issue I'll try again on this target. Cheers!!

[daemon]

Doh! I realised the last version was far too contrasty….so here goes with a definite final attempt with this data. Tried to be a bit mores subtle. Enough now.