NGC6888 - "An unusual Crescent!"

Paramount · Post by **Paramount** » Sat Jul 16, 2011 7:35 pm

Hi
I had previously taken some Ha and OIII data on this and managed to get out and get 3 hours of SII data in 30 minute sub frames. Normally I process my narrow band images using the HST palette partly because I prefer it but also because it is more scientifically correct in that the filters are asigned in order of wavelength, but I found that using this palette the OIII envelope that surrounds the main nebula didn't show up very well so I changed to a palette commonly used by the Canada France Hawaii Telescope (CFHT) where the filters are asigned to RGB in the order of Ha:OIII:SII.
This was taken with my current set up of Takahashi FSQ106ED at f5, Paramount ME and Starlight Xpress SXVF H9 with exposures of 7x30 minutes for Ha, 8x30 minutes for OIII and 6x30 minutes for SII, I would have got more SII but clouds interrupted the session. The master frames were colour combined in Maxim DL with a weighting of 1:2:7 for Ha:OIII:SII and processed in Photoshop CS2 using levels and a series of 'S' shaped contrast curves, in order to better distinguish between the main nebula and OIII envelope I used selected colour to shift the colour balance.
All three versions (Ha, Ha/OIII and CFHT palette) can be seen on the Nebulae 2 page of the image gallery of my website
http://www.imagingtheheavens.co.uk
and there is a full size image at the following link
http://www.pbase.com/image/136460025/original
Thanks for looking
Best wishes and clear skies
Gordon

kochu · Post by **kochu** » Sat Jul 16, 2011 10:05 pm

Great image Gordon.

Kochu

Post by **Airconvent** » Sun Jul 17, 2011 10:28 am

I do love such objects when they are taken in colour. Brilliant, Gordon! [smilie=cute.gif]

Tachyon · Post by **Tachyon** » Mon Jul 18, 2011 11:49 am

Impressive! Nice colors!

wucheeyiun · Post by **wucheeyiun** » Mon Jul 18, 2011 12:18 pm

Interesting ... i like it in colour too ... good work. By the way, how does it compare to HST processing?

Paramount · Post by **Paramount** » Wed Jul 20, 2011 3:46 pm

Hi
Thanks for the comments everyone, the processing is fairly similar to HST processing with the main difference being that the filters are just assigned to different colour channels so here the Ha=Red, OIII=Green and SII=Blue as opposed to the HST palette where SII=Red, Ha=Green and OIII=Blue. The processing workflow is exactly the same. The main reason for choosing a different palette is that some subjects such as this are better suited to one palette rather than another
Best wishes
Gordon