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Saturn 6th June - any advice to help tackle CA?


ilove1995
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It's been about 6 weeks since I last got to capture Saturn but managed to get a session in last night with my mak127 and SPC900. This capture is the result of 3000 avi's via a 2.5x barlow. Pre-processed in PIPP with stacking via AS!2 and wavelets applied in Registax 6.

The image has come out better than I expected. I'm not surprised to see the amount of CA in the image taking into consideration how low Saturn is in the horizon plus the fact that I used a 2.5x barlow. I'm hoping though that someone can help me out with reducing the amount of CA in the final image whilst keeping the detail I've managed to pull out using wavelets (i ran an RGB align before applying wavelets).

I have GIMP 2 installed on my pc and also an old copy of Photoshop (version 3) on my macbook. Could someone advice me on what steps to take to remove some of the CA? If anyone has the time feel free to have a bash at improving the image I've attached.

Despite the CA I'm happy with what I managed to get out of the mak 127 last night. :smiley:

post-26155-0-54069600-1370592639_thumb.j

Al

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Hi Al,

I'm no photoshop/gimp wizzard - but might be worth debayering the video with PIPP and then align andstacking each channel and using Gimp/CS3 or WinJupos. There does seem to be a strong blue cast overall, so perhaps a little play with the levels curves on each channel prior to merging/flattening. Then perhaps a quick denoise and adjustment of colour balance.

Nice capture BTW.

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I never thought CA would be an issue on a Mak - the meniscus shouldn't have enough curve to cause this. I'd start looking at other causes. Maybe a better barlow if you are using one? (prevention is better than cure)

Edited by haitch
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I never thought CA would be an issue on a Mak - the meniscus shouldn't have enough curve to cause this. I'd start looking at other causes. Maybe a better barlow if you are using one? (prevention is better than cure)

This looks like Atmospheric Dispersion rather than traditional CA which will be very pronounced given Saturns low elevation, though a poor/achromatic barlow might also be an issue. There's an excellent article on Atmospheric Disperson by Martin Lewis here http://www.skyinspector.co.uk/Atm-Dispersion-Corrector-ADC%282587060%29.htm

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Oh yeah - just clicked on the image to get the larger version and it's really apparent - I've only been doing Saturn visually and haven't really noticed any CA - but then that's probably just my eyes! 8-)

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That looks like the blue channel is completely misaligned to me. When you do your RGB align in RegiStax I think you will need to manually align the blue channel to get it correct, the automatic alignment does not always work.

Chris

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Nice image Al, no expert but I'd try the RGB align again in Registax, usually does a pretty good job.

Maybe download Registax 5 to see if it makes a difference to 6

Which Barlow by the way?

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Thanks everyone for the tips & advice. I'll have another go with setting RGB align in registax (trying both 5 & 6). If that fails I'll play with the blue channel settings to see if that improves things.

Gary, I use a 2.5x Revelation barlow. I'd like to purchase a better quality 2x barlow at some point but I'm not aloud to spend any more money on this hobby at the moment. :smiley:

Al

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The Revelation APO barlows get very favourable reviews for visual and imaging - I have both the 5x and 2.5x (which arrived this Tuesday). Build quality is excellent and both compare favourably against my Baader Zoon x2.25. My only complaint is that I am barely getting 2x from the 2.5x, even with the camera gripped at the very end of the nosepiece - though nothing a short extension tube won't fix.

There's a good review of the Smart Astronomy branded version and comparison against the equivalent power TV Powermates here Astromart Reviews - SmartAstronomy 2.5x and 5x Barlows

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ok so I tried a mixture of RGB Align and also some manual adjustment of the Blue channel and managed to get this out of Registax 6 (also went more extreme with wavelets)...

Still a slight tinge of Blue but an improvement on the previous image...

post-26155-0-44400000-1370619486_thumb.j

Al

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ok so I tried a mixture of RGB Align and also some manual adjustment of the Blue channel and managed to get this out of Registax 6 (also went more extreme with wavelets)...

Still a slight tinge of Blue but an improvement on the previous image...

That's made a massive difference - and there's stacks on detail for the image size. Good result.

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The second image is a huge improvement, and a great result from the Mak :)

If the dispersion is too pronounced a RGB align won't cure it though it deals with a few pixels in each colour very nicely. If it really bothers you an Atmospheric Dispersion Corrector will help, but start saving :(

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