NGC 6996, The Network Nebula
NGC 6992, also known as the 'Network Nebula', or 'Eastern Veil', is part
of the Veil nebula complex in Cygnus.
It's a supernova remnant, from a star that exploded about 5000 years ago,
and is roughly 1400 light years away (distance measurements vary and are
being refined all the time.)
This is the most technically challenging image I've done to date, and
is composed of 4 main frames, each comprising of Ha, OIII, Red, Green
& Blue, a total of 19 frames (Ha was 3 frames).
This meant that 5 separate mosaics using 2 different scopes were made,
then registered using Registar, and aligned with Maxim. The mosaic sections
were built using Maxim also.
The Ha was captured using the TMB152 @ F8 with an SXV H16, and the OIII
& RGB used a William Optics 80FD and Atik 16HR @ F6.9.
The main nebula image is built up using an Ha luminance layer, Ha for
red, Ha/OIII at 50% each for green, and OIII for blue.
A star layer was created separately using the RGB data and added to the
narrowband data then the whole of this was then dropped into the RGB star
background and the narrowband data erased except for the nebula itself.
There were a couple of small bits at the very edges where the frames left
gaps, and, rather than spoil the composition by cropping too closely,
I've copied some random starfield sections and pasted them in
don't treat this as a scientifically accurate image of the whole region
do pretty pictures
Dual scope imaging isn't quite as straightforward as it at first seems,
and with this image I had issues with my green subs being slightly out
of focus, causing green halos, and some flexure with the WO scope.
Also, as I'm using the 4 megapixel H16 image as the reference, and increasing
the size of the 1.4 megapixel 16HR image to match, the 16HR RGB stars
end up quite a bit larger than the H16 stars, especially as stars in Ha
tend to be small at the best of times.
Also, my flats were useless, so I initially had gradient issues between
the different frames which have taken much head scratching to deal with.
All a good learning process though.
This is my first image of the Network Nebula, and was imaged on the 25th
and 29th November(Ha) and the 9th December 2008(OIII).
This is Ha (red), synth Green (Noels' actions) and OIII (blue). No luminance
layer was used.
I played around with the processing for about a week, and ended up with
a very over-processed version, which I decided to scrap and start again.
One side effect of pushing my original attempt at processing too far,
was that I seem to have caught a 'bow shock, a shockwave from the original
I've cropped this section and included it too, as I find it very interesting
to see the red Ha shockwave, and right behind it the blue colour from
This has Ha used as luminance
Click on image below for full size
Imaged on several night during September 2009.
Imaging time was 22 hours 36 minutes.
Ha. 10 hours
OIII 7 hours 50 minutes
Red. 88 minutes
Green. 94 minutes
Blue. 90 minutes.
Telescope. WO ZS80FD
Camera. Atik 16HR
Ha 20 x 8 minutes
OIII 9 x 8 minutes
Subs all unbinned.