13 replies to this topic

[birddog99]

Was wondering if you guys can take a look at this PI WBPP image at the bottom. It has been cropped, DBE and Color Calibration have been applied. No noise reduction has been applied. What could be causing the orange halo's at the bottom of the stars and also what is causing the significant purple color blotches. I even did a manual preprocess to see if there might be stacking/calibration issues. Same thing. Could it be optical? Focus? As far as focus, I use SGP and it's auto focus routine. I get consistant V-curves and focus every 2 hours. V-curve usually in the 93% quality range. I checked with a batinov(sp?) and looked spot on. As far as optical, Tilt? I included a flats contour. Does this indicate significant tilt? Thanks for your replies in advance

 

Image Stats:

 

55 X 180sec lights

30 darks

25 flats

25 dark flats

 

Camera : ASI2600 MC Pro, Gain 0(unity)

PHD2 Guiding

 

Bortle 4-5

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Edited by birddog99, 24 February 2021 - 10:15 PM.

[Midnight Dan]

Maybe I'm blind :-) but I'm not seeing the orange haloes or purple blotches you mention.

 

-Dan

[birddog99]

Maybe I'm blind :-) but I'm not seeing the orange halos or purple blotches

Let me provide some better examples. I'll work on that tonite. They really show better after saturation.

[birddog99]

So here is a somewhat processed version. Was able to process out the purple color blotches, however if you will notice the stars  have a yellow area at the bottoms. Hope this helps

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[Midnight Dan]

Seems pretty slight.  Could just be atmoshperic dispersion.  If your imaging session started or ended when the target was lower on the horizon, you might be getting that in some of your subs.

 

-Dan

[birddog99]

Seems pretty slight.  Could just be atmoshperic dispersion.  If your imaging session started or ended when the target was lower on the horizon, you might be getting that in some of your subs.

 

-Dan

Here's a super zoom of a couple of those stars. What's strange is that the blue stars have the artifact at the top of the star vs the orange stars having it at the bottom.. I did start imaging pretty low on the horizon. Good to know that may be the cause. Not sure how to fix that in processing, except maybe desaturate the offending stars.

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Edited by birddog99, 25 February 2021 - 08:30 PM.

[Midnight Dan]

Yeah, atmospheric dispersion will create a blue-ish fringe on one side and a red/yellow fringe on the other.  Of course, blue stars have more blue light so the blue fringe will be more obvious, while yellow stars will highlight the yellow fringe on the opposite side.  

 

If they all aim in the same direction across the field, then it's likely atmospheric dispersion.  If they were all aiming towards the center, for example, it would more likely be a problem with the optics somewhere.

 

-Dan

[birddog99]

Yeah, atmospheric dispersion will create a blue-ish fringe on one side and a red/yellow fringe on the other.  Of course, blue stars have more blue light so the blue fringe will be more obvious, while yellow stars will highlight the yellow fringe on the opposite side.  

 

If they all aim in the same direction across the field, then it's likely atmospheric dispersion.  If they were all aiming towards the center, for example, it would more likely be a problem with the optics somewhere.

 

-Dan

Thanks Dan. Lesson learned. Was so exited to get one night of good conditions. Doesn't happen very often here in Houston. Shoulda waited another hour to begin the imaging.

[bloom691]

Did you use PCC (Photonetric) for color calibration? Just curious how much that would help or not.

[Rasfahan]

You can try to separate the RGB channels and realign them with distortion correction enabled to an artificially generated star field. With that I have removed a small dispersion effect successfully.

[Tapio]

I would have missed the problem if not pointed at it.

But I agree of the problem cause.

[birddog99]

Did you use PCC (Photonetric) for color calibration? Just curious how much that would help or not.

Yea, I used PMCC, the AUTOCOLOR Script, and the old fashioned way, which was to do a BN and CC separately. Even did the linear fit method. All the same

 

I would have missed the problem if not pointed at it.

But I agree of the problem cause.

You know, been doing this for 4 years now and I learn something new on every image I process. I've had folks tell me I'm my own worse critic. I think they are right. But that being said, this is the coolest hobby in the world.

 

You can try to separate the RGB channels and realign them with distortion correction enabled to an artificially generated star field. With that I have removed a small dispersion effect successfully.

I'll try that

[Midnight Dan]

You can try to separate the RGB channels and realign them with distortion correction enabled to an artificially generated star field. With that I have removed a small dispersion effect successfully.

The only issue you might have though is that it's likely only some of your subs that had the dispersion in them.  So in some of your frames, the planes would be align, but not in others.  When you combine them, you'll get a range of alignment accuracies, so the result will spread out the image in a given plane rather than it just being consistently offset.  So trying to realign the planes might not help.

 

If you really want to get rid of it, you might have to go back to your subs and remove those that were too close to the horizon.  But yes, I think you're your own worst critic! :-)  It's a pretty subtle effect and doesn't really detract from your image IMHO.

 

-Dan

[birddog99]

The only issue you might have though is that it's likely only some of your subs that had the dispersion in them.  So in some of your frames, the planes would be align, but not in others.  When you combine them, you'll get a range of alignment accuracies, so the result will spread out the image in a given plane rather than it just being consistently offset.  So trying to realign the planes might not help.

 

If you really want to get rid of it, you might have to go back to your subs and remove those that were too close to the horizon.  But yes, I think you're your own worst critic! :-)  It's a pretty subtle effect and doesn't really detract from your image IMHO.

 

-Dan

Thanks Dan. I really appreciate your help, and the others too.