NGC 7090 - Help needed with RGB composite

[rogerg (Roger)]

G'day all,

A couple of weeks ago I took a few shots of NGC 7090 and am having trouble getting any nice colour variation out of them. I'm not sure why.

The sharpness of the data was good - the nights were nice and clear, and very stable.

I have relatively little experience with combining RGB. I know that I need to measure the exact ratios of my filters by exposing a star of the correct spectrum, which I haven't done. But in the past for some shots such as NGC 1566 I've at last ended up with something better than I have here.

There just seems to be no significant variation between the colour exposures to generate any reasonable amount of contrast between the colours. Yet I look at other shots of this galaxy on the web and there's some nice variation.

I've set the image background to a neutral colour using levels, and used levels and curves to brighten the image, but other than that not done any processing on the stacked (average) files.


I realise my RGB exposure times are short, 40mins max per channel, but surely there should still b some variation apparent, just noisy?

I'm happy to send anyone the 4 stacked LRGB fits if they want to help (all the FITS if you like, but doubt that's necessary).

Full details:
L= 125 mins (100mins of 10 min subs, 25 mins of 5 min subs, two sets averaged then added/summed two sets together)
R,G= 40 mins each
B= 30 mins (one blue was trailed so excluded)

Individual exposures of 10 minutes in all but the 5 luminance at 5min, Luminance all at 1x1, RGB at 2x2 and resized to 1x1 for processing. Approx F/7.5.

Attached is my best effort, which is essentially a yellow grayscale image

Thanks for any assistance

Roger.

[bmitchell82 (Brendan)]

Ide love to be able to chime in here and give you some magical advice, but alas im a OSC man. It also looks as if you have some big comet tales coming off your stars.?

[Martin Pugh]

Hi Roger

fire them over and I will take a look and offer what advice I can.

martinpugh@bigpond.com
cheers
Martin

[rogerg (Roger)]

Originally Posted by bmitchell82

Ide love to be able to chime in here and give you some magical advice, but alas im a OSC man. It also looks as if you have some big comet tales coming off your stars.?

Not exactly sure what's caused the odd star spikes in the image. it's not comet tails from coma I don't think - stars are perfectly round across the field when out of focus, and in other exposures I've done don't show this distortion. Across this exposure the spike is always the same (direction and proportional length) across the stars in the FOV< not like you see with coma and them trailing towards the edges... from my experience. I need to do some more tests, see if it occurs in other imags or if there was just something in front of the telescope for those exposures.

Originally Posted by Martin Pugh

Hi Roger

fire them over and I will take a look and offer what advice I can.

martinpugh@bigpond.com
cheers
Martin

Thanks Martin, I will take up your offer, I just haven't the time at home yet..

[bmitchell82 (Brendan)]

its definately not coma... because thats a radial abberation, like you said they all tend the same way ~40 - 50 deg

also looks like saturday might be a fizzer makes me sad