NGC 6992 "Veil portion" in Ha and OIII bi-colour

[GordonH]

Hi all

Well according to the records August has been the wettest month on record and I can believe that. The weather was looking a bit more promising last night and following a suggestion from a fellow imager I had another go at NGC 6992 but this time I added some OIII data to it to make a bi-colour image. Luckily the sky stayed cloud free long enough to get 9x10 minutes unguided subframes for each channel. The seeing was poor due to very faint mist in the air later in the evening and the sky never got totally dark despite no moon being present. The subframes were dark subtracted (10 darks), then aligned and combined using median combine in Maxim DL and then the two resulting master frames were colour combined in Maxim DL using Ha for red and OIII for green. The resulting colour image was then processed in Photoshop CS2

I have enclosed the full widefield version as well as a cropped closeup

Thanks for looking and hoping for a better September

Best wishes

Gordon

[Paxo]

Excellent image Gordon, just glad someone somewhere has managed to get out.

Steve..

[Roy]

That's a really nice image Gordon

Forecast here for last night was for clear skies but all we got was red skies

[GordonH]

Hi Roy

Thanks for the comments, the forecast for where I live was cloudy for last night and it was clear for 4 hours (where do they get these forecasts from?)

Best wishes

Gordon

[markcol]

Very nice image, Gordon.

Mark

[Psychobilly]

Nice one Gordon,

I haven't had a chance with the weather all week. It was looking ok'ish around 9 pm but was total cloud cover by 10 pm

[Beyond_Vision]

Oudles of nebulosity picked up in this very pretty image. The colour though looks very unnatural.

Regards

Kevin

[GordonH]

Thanks for the comments everyone, regarding the unnatural look of the colours you have to remember that we see in RGB which means that any other colour palette such as emission line filters, Hubble space telescope palette, infra red, etc. will look unnatural to our eyes. The problem with RGB is that it masks some of the details that are clearly evident in the Ha wavelength for example and this is where emission line imaging comes in, ie it brings out detail that would otherwise be lost in standard RGB and it also allows you to image when you have light pollution or when there is a full moon

Best wishes

Gordon

[Psychobilly]

Just in case anyones wants to try tweaking the colours..

Its possible to change the colours in Ps/CS ... using...

Image -> Adjustments -> Channel Mixer -> and working on the Red and Green output channels independently adjust the HSI Values.

As Gordon has already said color for DSO's is pretty subjextive and most people will process for soemthing that looks good rather than a physically accurate colour.

To be pysically accurate you could adjust the colors for O III (500.7nm) and Ha (656.3nm)

Billy...

I still think its a really amazing image

p.s. I have been looking for emission sectra photo's...so you can see the "true®" colours...

Hydrogen...

http://hyperphysics.phy-astr.gsu.edu/Hbase/hyde.html#c4

and these...

http://astro.u-strasbg.fr/~koppen/discharge/

still looking for a good O III one...

[narrowbandpaul]

very true gordon, any image not in RGB will be odd to our eyes. And as you say, NBI really brings out details otherwise missed with conventional RGB. I couldnt agree more...

Super looking image...the TMB is certainly performing well isnt it?

How did you synthesis blue...did you use 1/3 Ha for blue to simulate Hbeta..

Great Image again

Best Wishes

Paul

[GordonH]

Hi Paul

Thanks for the comments. In this particular image there is no blue channel, it is purely a two channel colour image, this can be done in Maxim DL before processing in Photoshop CS2, now talking about synthetic blue channels and the like

Since posting this image I had a couple of suggestions about adding data to obtain a blue channel so I have tried two methods

1. Creating a synthetic blue channel from the red and green channels using Noel's tools in Photoshop CS2

2. Using existing OIII in the blue channel and creating an RGB image in Maxim DL and then processing it in Photoshop CS2

I have posted the images on my website http://www.imagingtheheavens.co.uk in the nebulae section of the image gallery along with the other images for comparison, I would be interested to know what people think

Best wishes

Gordon

[narrowbandpaul]

for making an RGB image from narrowband data I use the technique pioneered by Richard Crisp(seems like a good choice!)...he uses...

1/3 S[iI] + Ha for red

O[iII] for green

O[iII]+0.34Ha for blue

The 0.34 comes from the naturally ocurring ratio of Ha to Hbeta...Hbeta=1/2.92Ha.

This technique seems to work pretty well. Like he says, you have to get the Hb flux in the blue channel

Obviously you dont have the sulphur data, but for most objects 1/3 S[iI]=0

Although you could also try HaO[iII]O[iII] for RGB, but the inclusion of some Ha could be good.

Hope this helps

Do you plan on adding sulphur?

Best Wishes

Paul

[narrowbandpaul]

Gordon,

The colours really do look fantastic in the 2 channel colour only

Superb

Paul