2 replies to this topic

[Tapio]

Still learning the ropes with this color camera.

 

Have now used AA7 and APP for stacking and with both I end up with image where color channels are not aligned.

I can align those easily with split channels and combine & align but can someone give a reason why is this happening and is there a feature for channel align in processing ?

 

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[jdupton]

Tapio,

 

   If the color shifts of any given color are all in the same direction across the frame, the most likely answer is that the cause is atmospheric dispersion -- caused by refraction of the light passing through the atmosphere. Since the air mass you image through is thicker towards the horizon, the atmosphere acts like a weak prism and separates the wavelengths slightly.

 

   If the direction / orientation of one color is always towards or away from the center of the frame, then the most likely cause is a form of chromatic aberration in the optical system.

 

   As you stated, the first cause can be corrected by simply separating and then realigning the color channels via translation. The second cause can be treated if the software you use has a chromatic aberration correction function. It can be treated by separating the color channels and then applying a magnification or shrinkage factor to each channel so that each now has the same image scale and then recombining.

 

   We would need to know what software you use in order to tell you whether the feature is present. (EDIT: Sorry, now I see that you use either AstroArt or AstroPixelProcessor. I am not familiar enough with either of those to advise how to treat this.) In PixInsight, there is a Channel Match process (Menu: Process | Geometry | ChannelMatch) that allows you to move one channel with respect to the others without splitting the image apart by channel. Adjustment can be made in tiny sub-pixel increments for best results. In PixInsight, CA can be (more or less) fixed by separating the channels and the running Star Alignment with distortion correction enabled.

 

 

John

Edited by jdupton, 27 January 2022 - 03:08 PM.

[Tapio]

Thanks John.

I have been imaging with mono camera over 10 years. Before that i had color cameras and I don't remember seeing this kind of problem then.

 

So why can't processing software do this on the fly ?

Edit: found this thread on APP:

https://www.astropix...ng-of-the-stars