Double comet after a stack...

[Ant]

I took some images of the comet the other night and I've managed to stack them is various manners.

But for one of them I wanted to show static stars and a long smudge for the comet... for some reason I cannot get DSS to give one one Comet?

I've manually been through each frame and checked and cannot see anything much wrong - but as you can see it looks like the comet has split in two - but it hasn't I've checked

Any suggestions?

Cheers

Ant

[Ant]

anyone?

[Uranus]

Bueller Bueller Bueller?

[Dave]

Ant,

I have seen something similar (but not quite as pronounced) when stacking with comets in the frame. I never found out what caused it.

[Ant]

Thanks mate. It is odd... I've tried manually selecting the a star to stack on in each frame - but it doesn't get any better.

I guess I'll start stacking smaller groups and see if I can do it that way

Cheers

Ant

[garethmob]

isnt there a comet part in DSS to help that ant ?

[Ant]

Yeah I've managed to get the stars and comet to stack separately (using the comet and star option in DSS), but I wanted to show the comet motion over the course of three hours...

The sort of finished images are attached. It was a standard stack in DSS that I really wanted, and it doesn't want to play ball.

Cheers

Ant

[garethmob]

ahhhh well it does look really really good ant is it in colour or mono?

[Ant]

It's a mono CCD >>this one<<

Although it's a slightly older version.

Cheers

Ant

[FraserClarke]

The stacking software has rejected the core of the comet, because it thinks it is a hot-pixel or similar (bright in some frames, but not all). It doesn't reject the wings of the comet, because they don't come above the threshold. So you end up just seeing the two wings without the core, and it looks like a double comet. I guess you're using a "sigma-clipped" rejection algorithm when combining the frames? (I don't use DSS, so I don't know exactly what they'd call it unfortunately). You'll have to play with the rejection thresholds (again, no idea how to do this in DSS unfortunately!). In other software, I'd probably use an average just rejecting the brightest 1 or 2 values (depends how many frames you have). Or you could just align and average (no rejection at all) all the images. That will preserve the comet image, but will also probably leave other detector effects like hot pixels.

It's tricky, because you're trying to preserve something which to the software looks exactly like the kind of things we spend most of our time trying to get rid of!

[Ant]

Yes a Kappa Sigma Clip - I am going to re-run the stack now with an average setting.

Thank you - I'll post back shortly

[Ant]

Fantastic Thanks for that! I know have the result that I wanted!!

Going to re-stack using the comet and star and just comet selections and see what happens.

Thanks again!

Ant

[Simms]

Fantastic Thanks for that! I know have the result that I wanted!!

Going to re-stack using the comet and star and just comet selections and see what happens.

Thanks again!

Ant

Nice shot, but I much prefer the first set of images you posted - I love the `classic` comet images. Inspiring stuff though & nice CCD you have there.

[Ant]

So do I but I'm greedy and wanted the whole set.

1. Stars stacked and comet stacked separately.

2. Comet stacked streaky stars

3. Stars stacked and streaky comet.

I'm also working on an animation - just down loaded fits liberator to convert the fit to a tif so the animation software will work

Cheers

Ant