Centaurus A

[Gvarouha]

Finally sorted out frosting issues with my st2000xm, and managed to get a few hours between clouds.

This is my first time shooting with a ccd so am still getting used to the setup, but pleased with the results

Shot with skywatcher ed80, heq5 using astrodon LRGB

Comments and criticisms welcomed. Cheers

[raymo]

Hi George, nice job. Only comments I've got are the elongated stars, which
I imagine is down to tracking, and it looks like you've overdone the
sharpening a bit, judging by the dark haloes around the less bright stars.
raymo

[Gvarouha]

Cheers Raymo,

I never quite know when to call it quits with the sharpening.

The elongated stars have been giving me some serious issues. I can take a 5second or a 15 minutes exposure and the stars look the same.

I've worked on my polar alignment and it's pretty spot on and my guiding graph only shows 3" peak to peak.

[Atmos]

Someone should correct me if I am wrong but that could be caused by flop or flexure in the focuser.

[raymo]

If you get the same elongation regardless of sub length, then Colin will be
right, the camera sensor is not perpendicular to the light path, either as
Colin said, focuser sag, or maybe at the connection between the camera and the optical train. I also noticed that you have blue semi haloes over the
top of the brighter stars, which seems likely to be CA from something in the optical train.
raymo

[Atmos]

The ED80 is a F/7.5 doublet so it will have CA but it would likely be made a lot more prominent by whatever is causing the star elongation.

[Gvarouha]

I never thought of sag.

When I have my DSLR on the back with a wider FOV I notice the stars are much worse in the corners and elongation tends to be more fanned out in different directions. A flattener may help with this but I always had a sneaking suspicion something else is at play.

Is there anyway to diagnose flop, maybe rotating the camera to see if the orientation of the elongation changes?

[Atmos]

If you rotate the camera and the stars streaking remains in the same direction then you can guess that it is directional. It should also change when you point at different parts of the sky if it is focuser sag.

[rustigsmed]

hey George,

congrats on first light!
very promising start!
what was the imaging detail break down?

russ

[Gvarouha]

Hey Russ,

27 x 300sec of RGB combined @ 0C
40 x darks
40 x flats
100 x bias

[rustigsmed]

thanks George, capturing Luminance will help you out a lot as well.

cheers

russ