Author Topic: Unable to star align narrowband data after multiple trys - please help  (Read 739 times)

Offline girishkum

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I'm still relatively new to pixinsight and astrophotography. Trying narrow band imaging now and struggling with star alignment - not sure if i'm doing something wrong with my acquisition technique. I'm attaching recent helix nebula Ha, OIII images in zip files calibrated in pixinsight (xisf files). Also attaching a subset of Ha for pacman. In both cases, i get the no putative star matches found despite chaing RANSAC parameters and log sensitivity in star matching and increasing layers in star detection. Any help would be deeply appreciated.

Equipment: Celestron 6 SCT with f6.3 reducer and guidescope / phd2; ASI183MM Pro cooled to -15c; ZWO filters

Helix Ha (
Helix OIII (
Pacman Ha (


Offline astroedo

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I've tried to align your pictures.

The problem is that they are completely out of focus, the stars have a donut shape an even with Peak Response set to 1 it is impossible to match the stars.
The out of focus problem has a secondary drawback: due to the ling focal length, yoo can see only a few stars so PI cannot get a suitable set of putative stars.

I'm sorry but I suppose that the only way to aling your set is to performa one by one alignement with DynamicAlignement.



Offline girishkum

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Thanks Edoardo. I see the donut shape in the helix nebula - however, do you think the pacman Ha data set is out of focus as well? The stars don't seem to show the same donut shape there.

I just installed robofocus on my system - need to figure out what's happening.


Offline msmythers

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Fix the focus. It's bad for all 3 sets.


Offline dld

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Hello Girish,

Unfortunately the Pacman images are also out of focus. However, I had some success by using the attached settings.