Reduced CA without AI

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Jeff Dyben avatar

I tried an old (as I’ve now learned) method, fueled by frustration, to reduce chromatic aberration in my images. I’m shooting with a Explore Scientific ES-ED102, a ZWO ASI 2600MC PRO, and an Optolong L-Para.

The Method: After loading the final stacked image into PixInsight, I ran it through my CE script to isolate Ha and OIII. Once there, I used Ha as a reference and ran it through Star Alignment again. Since the aberration was consistently in one direction, it “nudged” the colors to fit. I attached results of this below. I believe it only works because I’m dealing with lateral chromatic aberration, for purple halo’s I’m not sure.

Applied method on the left, old on the right. Pointed out a bad star to demonstrate difference as best I could. I got the stretches approximately as close as I could. Along with fixing multi-colored stars, it also helped to make the star shapes more circular instead of elongated.

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Andrea Tasselli has let me know that this is already an established method for reducing CA (thank you!). I’ll leave this thread up in case anyone else newish like myself could benefit.

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andrea tasselli avatar
Yes, an old method from the bygone days of CCDs.
Jeff Dyben avatar

andrea tasselli · Feb 7, 2026, 03:42 PM

Yes, an old method from the bygone days of CCDs.

I expected as much. I updated my description to account for this, thank you for letting me know!

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John Hayes avatar

There are two types of low order chromatic aberration: longitudinal and lateral. Longitudinal is caused by the variation in focal length with wavelength and lateral is the variation in magnification with color. So, when you re-align the channels it’s important to specify that the fit should correct for “distortion” since the misalignment between channels will resemble geometric distortion (which is another 3rd order optical aberration).

John

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