Hi all

After an abysmal May as far as weather is concerned I have finally got my filter wheel up and running and as the sky was clear last night (it was up till mn) I thought I'd chance my luck and have a go at the Pelican nebula. After I got everything aligned I was ready to begin just before 12mn but as the camera was taking its dark frame for auto dark subtraction patchy clouds started rolling in from the southwest and this was the pattern for much of the rest of the evening. I decided to stick with it though and managed to shoot 7x10 minute unguided each of Ha, OIII and SII (the last one of the OIII and SII had to be junked because daylight stopped play). The was a period of about an hour when there was no cloud at all but the rest of the time patchy clooud came very close to cygnus and on a few occasions covered where I was imaging (thankfully only for a few seconds each time)

I combined the 6x10 minute SII(red), 7x10 minute Ha (green) and 6x10 minute OIII (blue) Hubble palette style. Onle 3 small iterations of curves were used as well local area contrast in Noels tools. No levels were used. Considering the rush and the threatening cloud I am well chuffed. I have also enclosed a cropped close up of the Pelicans "neck" to show the chimneys a bit better.

Thanks for looking

Clear skies

Gordon

Great colours.... Just seem a bit grainy in places though ....... i wonder what caused that.Maybe some dew problems?..Did you take flats,darks?

Looks more like a chicken in flight to this monkey. Beautiful colours by the way, how close are they to 'real' (as in what is seen in visible light)?

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Hi Guys
Thanks for the comments, I think the grain is due to not enough exposure and subframes and then being over processed, dew is definitely not a problem as I check that periodically during the night and the dew heaters are working fine. Intermittent cloud may have had some effect but it is difficult to say. I used basic auto dark subtraction in Maxim DL where Maxim instructs you to cover the camera for the same length as your exposures then it takes one darkframe and subtracts this from each subsequent exposure as it is downloaded, no flats were used. The colour is completely different to what it would look like in visible light as I was using the hubble palette. As it is predominent in Ha the nebula will appear mainly red in visible or RGB light exposures.
Regards
Gordon

Gordon,

I've found that there is sufficient noise in a single dark frame on my ST-10 that the auto-dark functionality can introduce noise. While I don't go crazy with darks, I've built up a library so that I typically use about 10 darks, sigma combined, to create a master dark and use that for subtraction.

My camera has been very consistent in its dark noise over time, so the library approach has worked well.

Clear skies,

--Andy

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Observatorio de la Ballona

Hi Andy
Thanks for that tip, it was actually one of the many things on my agenda to try out along with flats etc, but you have reminded me that I need to get and do it
Cheers
Gordon