Author Topic: NGC6960 Western Veil Nebula  (Read 68 times)

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MarkS

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NGC6960 Western Veil Nebula
« on: Aug 12, 2018, 11:53:55 »
Here's my version of the Western Veil Nebula - it's been a popular OAS target this year!

2 hours of data in 30sec sub-exposures.  Sony A7S on Celestron C11 with Starizona LF Corrector at f/7.2. SQM average was around 21.0  Bayer Drizzle Integration was used.  Even though it doesn't sharpen features at this imaging scale, it does give a much better noise profile i.e. the background noise has a finer granularity.



Here's the larger version:
http://www.markshelley.co.uk/Astronomy/2018/NGC6960_20180810.jpg

I think the star shapes across the whole image are about as good as I'm going to get them with this scope and corrector.  There is still obvious chromatic aberration but not too severe. They're just not up to Takahashi standards!  However, to get better than this at this image scale I would probably have to buy a corrected Ritchey Chretien or equally expensive optics.

One other trick I did during processing is worth sharing.  Instead of doing a single ArcsinhStretch, I performed 3 successive ones each with a stretch factor of 4.  The image responded much better to that strategy.

Two other complications:
  • This corrector is extremely sensitive to collimation issues. I have to slew to the area of sky I'm imaging and then take a few test images, adjusting the collimation by examining the star shapes in the corners.
  • The flat frames MUST be taken with that identical collimation and with the scope pointing to the same place in the sky. I've built a contraption to hold my diffusing panel in place against the dewshield.

Mark


« Last Edit: Aug 12, 2018, 12:12:13 by MarkS »

Carole

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Re: NGC6960 Western Veil Nebula
« Reply #1 on: Aug 12, 2018, 13:25:41 »
Lovely image Mark.

As for the technical stuff, that does sound like  lot of hard work - as if imaging isn't difficult enough at times anyway, but if any-one can do it - you can do it.

Carole

The Thing

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Re: NGC6960 Western Veil Nebula
« Reply #2 on: Aug 12, 2018, 19:28:41 »
Very nice Mark. I must do the Bayer Drizzle, I have all the PixInsinght drizzle files, just never used them for my version. I think  SCTs are really only suited to planetary imaging where only the centre of the optics are used.

MarkS

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Re: NGC6960 Western Veil Nebula
« Reply #3 on: Aug 12, 2018, 20:07:47 »
Quote from: The Thing
Very nice Mark. I must do the Bayer Drizzle, I have all the PixInsinght drizzle files, just never used them for my version. I think  SCTs are really only suited to planetary imaging where only the centre of the optics are used.

The moveable primary mirror is the Achilles Heel.  It's the source of all the problems.  I'm going to give it a fair go with this new corrector but in the end I think I'll give up, just to preserve my sanity.  The need to re-collimate and take unique flat frames depending on where in the sky you are imaging is a complete non-starter!  But there are some Autumn and Winter targets I really want to capture at this imaging scale.  M33, Horsehead, and Orion Nebula are at the top of that list  :D

Mark
« Last Edit: Aug 12, 2018, 21:49:54 by MarkS »

NoelC

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Re: NGC6960 Western Veil Nebula
« Reply #4 on: Aug 13, 2018, 10:30:31 »
Awesome image Mark
I read your collimation thread with great interest (although I'm using an RC). I hope you find a solution (glue the mirror in place and add a focuser?).

Noel
Synta mount, a bunch of telescopes and a shed (on wheels).