Comets

[Simon Pepper]

I am trying to process my third acquisition of comet data and yet again I am unable to do it. Spent hours stacking, aligning, messing about and the outcome with comets is always an utter mess. I have followed countless tutorials and none of them work for me. What am I doing wrong? Can anyone assist here or want to have a crack at my data? If not I will be buying Adam Blocks complete library as I have just about had it with these cold ice monsters!!!! 

Edited March 7 by Simon Pepper

[happy-kat]

Deep sky stacker got a comet stacker update last year and ASTAP I think it was this year, what are you using for processing?

[Elp]

My first go took some time, longer than DSO processing, my recent second attempt was quite straightforward.

Basic method is:

1. Take tracked shots against the starfield (either mount sidereal tracking or autoguided), it helps if your comet isn't moving around other than in a linear line from first frame to the last.

2. Stack with calibration frames, and when you register use comet alignment (I use Siril). You need to draw a selection box around the comet head in the first frame, press pick one box so it gets the x y info from your selection, then do it again for the last frame (you can open your image list via the multi tab looking button in the bottom right of Sirils main window).

3. Then stack all frames with a very narrow kappa sigma rejection range (you can experiment here to see what results you get), you'll have a comet stacked image.

4. Return back to your lights sequence and register again but using deep sky alignment, then stack again and you'll get a Starfield image.

5. Then do DSO pre processing such as background extraction (or you can do this to the image sequence prior to stacking), histogram stretches etc.

6. You then need manual image editing skills to do the rest. Comet image needs to be masked or you can delete all the blurred Starfield background, then layered on top of the good starfield image. Some creative work then needs to be done to eek out detail, blur out stacking noise and general cleanup.

 

[Clarkey]

My method is very different. If you are talking about the Adam Block videos, this suggests you use PI for processing?

For my (acceptable) comet image, I used a very different process.

1. Take the normal shots and then remove the stars from all the images using a batch process in PI. (This takes a long time)

2. Comet stack the starless images to give the comet stack. This will have some minor trails from where the stars were removed.

3. Process the comet image using masks etc to blur the star trails that remain.

4, Run a normal star stack to give you the star image. Remove the stars and add them back to the comet image as per normal processing.

There may be a better way - but as yet I have only paid for the Adam Block Fundamentals videos. The comet and Horizons is more expense....

Below is the result. (This was about the first image I had ever done in PI, so I suspect I could get better results now I know what I am doing with the software).

 

[Simon Pepper]

Thanks all I will try again when I have the patience. Criminally I did not take flats which has not helped and I have moved the camera orientation now but the master of the stars looks perfectly fine it’s when I come to try and stack the comet the issues occur. The left over from star trails is evident when stretching it’s a mess. As I said three comets in now and I still can’t figure it out. 
 

Where the hell is Russ with CometXterminator !

[Elp]

32 minutes ago, Simon Pepper said:

The left over from star trails is evident when stretching it’s a mess

You just need to apply a subtle motion blur perpendicular to the trail motion, and depending on how severe it is a slight minor gaussian blur. If you really care about the subtle flares around the comet head, mask it out prior so that part doesn't blur.

The intensity/thickness of the blurred star trails will also vary depending on your kappa sigma high and low values prior to stacking.

Edited March 8 by Elp