What an I missing about comet registration?

[dx_ron]

It sounds simple enough. Pre-process.

Select Comet/Asteroid Registration method.
Use the frame selector to load the first image of the sequence.
Draw a selection around the comet and click Pick object in #1.
Use the frame selector to load the last image of the sequence.
Draw a selection around the comet and click Pick object in #2.

At the end of this process, Siril should display a velocity vector in X and Y. Make sure the Accumulate reg. data box is checked and click on Go Register.

Yet, when I stack I still get stationary stars and a smeared-out comet. This is the stacked result along with the registration tab that got me there:

Related question: I also shot some images using “comet tracking” in PHD2, where the comet remains in the same position in the frame and the stars move relatively. Is there a way to register those frames on the comet?

[khoa.sus2 (Khoa)]

Are you following these general steps?

Register stars as normal
Stack with fixed stars
Re-register with comet start and end points. Are you hitting “go register” again?
Stack tracked on comet

If you tracked on the comet with PHD2, you can either trust its accuracy and stack as-is, or (probably a better idea) use the One-Star registration method in Siril, with the one “star” being the comet core. I’ve never tried that.

[maboleth]

1. Preprocess everything with a script
2. Set Home to Process dir
3. In Sequence pick pp_light_seq
4. Choose the best file in the list and calibrate that image to show real colors. Be sure to save it!
5. Register everything with Global Star Alignment (deepsky)
6. Stack with Average with Rejection, Additive Scaling, Winsorized Sigma Clipping and Sigma high and low 1/1. Save as ‘stars-stacked’
7. Go to Sequence again and check if r_pp_light is checked. Also check if the best image is still the same as it used to be, although now as r_pp
8. Register everything as Comet/Asteroid, but don’t engage yet.
9. Go to Sequence again, open Frame list again and pick the first image in the list.
10. Select a comet with your mouse, make a rectangle selection. Go to Registration again and click Pick Object in #1
11. Do the same as above in 9. and 10. but pick your last image in the list and use Pick Object in #2
12. Go Register
13. Stack as before but save it as comet_stacked filename

This way you will get two files - the stars and a comet. Editing further and stacking in Photoshop or GIMP you will get a nice, clean comet image.

Good luck.

[p088gll (Götz)]

I tried the One-Star registration method for C/2022 E3 today after using PHD2 to track the comet. I worked quite well

[dx_ron]

@maboleth

• Preprocess everything with a script
• Set Home to Process dir
• In Sequence pick pp_light_seq

I pre-processed manually, but I wind up here with a pp_xxx sequence

• Choose the best file in the list and calibrate that image to show real colors. Be sure to save it!

PCC fails - no stars found. I assume my subs are too short

• Register everything with Global Star Alignment (deepsky)
• Stack with Average with Rejection, Additive Scaling, Winsorized Sigma Clipping and Sigma high and low 1/1. Save as ‘stars-stacked’
• Go to Sequence again and check if r_pp_light is checked. Also check if the best image is still the same as it used to be, although now as r_pp
• Register everything as Comet/Asteroid, but don’t engage yet.
• Go to Sequence again, open Frame list again and pick the first image in the list.
• Select a comet with your mouse, make a rectangle selection. Go to Registration again and click Pick Object in #1
• Do the same as above in 9. and 10. but pick your last image in the list and use Pick Object in #2
• Go Register

I have done that, as can be seen in the screenshot above

Today I deleted the r_pp_xxx sequence and all the r_pp_xxx.fit files from the directory. I noticed that the comet registration screen does not have a “Prefix” box. During the registration process no files are written and at the end there is no sequence with registered images. This explains why previously my stacked image was still the one from the global stars registration, because that was still the only registered sequence in the folder.

[dx_ron]

@p088gll

I tried the One-Star registration method for C/2022 E3 today after using PHD2 to track the comet. I worked quite well

I tried this, but the comet moves so much that after only about 1/4 of my frames the algorithm locks onto an actual star. I went ahead and stacked those frames, but I’m not (yet) able to get any sort of reasonable color balance. Will keep working on that.

[Daniel_Catalina]

I am doing photometric calibration like this:

• open Stellarium, search for the object i have in the frame and set the time to approximately the time i to the picture
• i am using the field of view feature to get the approximate framing i had
• zoom in the middle of that frame until the stars start to show names
• use the name I find there in the photometric calibration window in siril

It does not always work at the first try, but I also did not had to do more than 3 tries.

Don’t forget to click get meta data from file (or set the correct values for focal length and pixel density by hand).

I hope this helps you.

[dx_ron]

Interesting. I shall give that a try.

I am still unable to get a comet-stationary registration sequence by following the tutorial steps.