Problems getting sub exposures to align

Reggie Jones

Hi Adam.  Took about 6.5 hours of narrowband data on NGC 7635 (Bubble Nebula).  I used WBPP to calibrate the data and then use Cosmetic Correction.  I checked the data via Blink and then manually aligned the sub exposures via Star Alignment.  I initially used Star Alignment at the base settings that are given initially when opening the process and without drizzle.  The result was that only 8 of 95 subs aligned.  I methodically changed the Star Alignment settings and ran it multiple times until I found limited success (36 sub exposures successfully aligned) with the settings shown in the attached file.

Not sure what the issue could be with the data other that some sub exposures showed signs of deformed stars.  Would like to have you take a look at the data and provide your thoughts on what the issue could be and suggestions on how to address and correct the problem.  My data can be found here - 

https://www.dropbox.com/sh/gghsv15vdekzypo/AADsTGAiWmq8_SQ9UPO1ZMw0a?dl=0

I processed the data that did align and got what I think is an acceptable image (attached) but it would have been nice to have all the data to use.  This was taken on my personal equipment from my backyard in Los Angeles.  Thanks in advance...

Reggie

BlockHead

Reggie,

There is something I do not understand. I seem to recall this issue..but I can't remember what it was about.

Why the weird subtraction at the borders?? This already looks odd to me. I don't understand what is going on there. (Is there some kind of overscan pixels??).

-the Blockhead

BlockHead

Reggie,

I was able to align the images in the first attempt.

I did do one adjustment that you may not have thought of?

You have different exposures through different filters- NB filters in particular. This is as harsh a situation as you can give StarAlignment since the combination of different exposures and different filters will make the stars look *very* different from frame to frame. 

I knew this going in. I knew the signal was going to be very faint. So I preemptively adjusted the sensitivity parameter all the way up to a value of 1. I felt confident about this since you apparently applied cosmetic correction.  Then I chose a random Ha from the 300s set as the reference.

It aligned all 95 frames in about 60 seconds on my computer.

Perhaps you can do the same?

I actually started to make a video thinking I would get the result you did... but then I actually succeeded...so I didn't save it. 

-the Blockhead

Reggie Jones

Hi Adam - I'm not sure what causes this - it is a regular occurrence with all the subs I take with my equipment with any of the 3 cameras I use (Mono & OSC).  It hasn't been a problem getting the subs to register in the past; I've added a folder with the subs that did align and another folder with the integrated Ha SII and OIII subs so you can review these as well.

Reggie

BlockHead

Update.

Actually... they all aligned with the default settings as well. 

My settings appear to be exactly the same as yours.

I cannot see your file names... make certain the files you loaded to be registered are the C_CC files! 

I can see you did that for the reference but not the others.

So..I do not currently see an issue.

-the Blockhead

Reggie Jones

Thanks Adam - you're right, I did not consider the sensitivity parameter setting nor the fact that with Nb, the faint signal would require this kind of adjustment.  Let me try that and I should come up with the same result you did.  I can then rework the data.

You have me thinking why my subs have this border subtraction happening.  I need to track down the answer to this.

Thanks Adam!

Reggie Jones

Response to your update - Thanks, I've made that mistake before...

Reggie