Heavy chromatic abberation

Hi Ruedi,

you can try to check the "align channels" and maybe "split channels" in the "2) calibrate" tab (way down in section "save calibrated light frames"

I always have those boxes checked.

Hi JuergenN

Thanks for the quick reply. 

had align channels on already, added split channels. This did not help, unfortunately.

Hi Ruedi,

I suggest your best approach to 'rescue' your above image would be to save the image as a TIFF file and then use the defringing capabilities of a good photo-editing package (for example, the Lens Correction module in Adobe Camera RAW) to moderate the visual impact of the green-purple dispersion produced by the Sony lens.

Beyond what has already been mentioned by Juergen I know of nothing else that you can easily do in APP.  I guess one could try to use APP's HSL selective color tool to achieve the same sort of result as the photo editing colour defringing tools but I think this would involve far more effort to find suitable settings.  In one of Mabula's early APP training videos he gives a demonstration of removing unwanted green from images using HSL selective color so I am sure the same could be done to moderate the  blue-purple tones opposite to the green in the stars.

I believe your Sony camera has a zoom lens which I guess you used at near maximum zoom-in and aperture?   You might try experimenting by shooting some high contrast subjects during daylight that by for example stopping down the aperature that the severe fringing you see can be significantly reduced.

Good luck and clear skies

Mike

@mestutters Hi Mike

thank you so much for your hints. In fact I played quite a bit around with different settings - with nearly no effect. I tried in camera raw the manua definge to get rid of the abberation effects. Will dig deeper there.
Indeed the Sony has a high quality Zeiss zoom lens, but like all these lenses it is built of im my case 18 elements. The fact that there are some extra low dispersion elements to prevent from abberation effects does not help to prevent from all of the effects. I use the same camera for infrared-photography, using different filters. In IR the best setup is to use the lowest "F" to prevent from hot spot effects (what would mean to have a higher illumination gradient in the flat frames).

I shot the images attached at 2/3 full zoom (400mm - 600mm is max). With 600mm I saw less of these effects when shooting Orion and Rosetta nebula. Have to analyse this further, too.

Next will be to improve the image quality by following your very useful advises and fill a matrix: Different step through apertures at different zooms to get a feeling about the influences of these 2 parameters.

thanks again for your hints!

clear skies

Ruedi

BTW: The pixinsight stacker does not produce artefacts that prominent (but still a pain, too), but the algorithm over all of APP does deliver miuch better results and the handling is better. 

Stacking through integration tends to make defects more noticeable—this is completely normal. Have you tried using BayerDrizzle?

/Stefan

Hi Stefan

thanks for the hint. Yes, the "defect" is relatively faint in one single frame, but becomes very prominent during stacking. BayerDrizzle does not help here. I did several stacks with different settings - always with very similar result. 
I am - after some more research - not even sure if it's really abberation I see, it could be caused by the Kolarivision 400...700nm filter I use (some diffraction, reflection...whatever). will investigate further...but I first need a Clear night.

Clear Skies, Ruedi

Hi folks...again. I am still lost with my images. I started to believe this is abberation, but I have my doubts. It seems to affect a certain class of stars. If anyone has a hint what it could be - any hint is welcome.

Thanks.

Hi all

I shot some frames using a 665nm filter from Kolari. I don't see the artefacts anymore - but the frame quality weakens obvousely. I think this is a mix of coma and chromatic abberation. 
Pixinsight does a better job regarding these artifacts - but the overall result of APP is much better.

I was wondering if there is any chance in improving the stacking algorithms.

Here an example (665nm, 40" frames, not well focused, full moon, no proper calibration frames...)