Newtonian telescope exhibits chromatic aberration?

[lrt75914]

Hey guys,

I've been trying trying to take an image of Jupiter with my Skywatcher Explorer 200 PDS. The seeing conditions were [removed word] poor and I had to resort to my parents garden as an observation site. There was a lot of light pollution and heat convection that made the imaging session a bit difficult. Nevertheless, I was able to capture enough material to end up with the following image of the gas giant:

I didn't use a barlow lens, so I was quite surprised to see some chromatic aberration in my final image.  My instincts tell me that this shouldn't happen, since there are only reflecting surfaces in the optical path, right? Furthermore, the image of the lunar eclipse that I captured with my fathers DSLR (attached to the telescope) seems to be devoid of any color fringes.

Could anyone give me a hint as to why this happened and what I could do to avoid this problem? Any input is appreciated .

Patrick

[RikM]

Atmospheric refraction will also give red and blue fringes at the edges of a bright planet, especially if fairly low down in the sky. Applications such as Registax have a tool to reduce this.

Nice image all the same

[lrt75914]

Sorry to double post but I forgot to give you a rundown of my equipment:

Telescope: Skywatcher Explorer 200 PDS

Mount: Skywatcher AZEQ 6

Webcam: QHY5P-II

Camera: Sony alpha 77 ii

[laudropb]

The colour fringing is almost certainly due to atmospheric conditions. Still. Given the conditions it's a nice image.

[Leveye]

There is a quick fix for this in Registax. Color alignment I believe. 

[lrt75914]

Alright, I gave the RGB Realign tool in Registax a shot and voilà

Thank you so much for the quick replies and kind words

[MarsG76]

I found that this happens with my Skyris 618C. Perhaps it happens with the OSC camera Bauer due to the color pixels not being aligned perfectly on the matrix and the high magnification exaggerates the effect.

When I capture using the 618C I always need to move the red channel 2 pixels up and left where the blue moves down and right by 2 pixels to align the RGB channels. I do this in PS. Not only does it get rid of the fringing/aberrations but it actually improves the detail.

[MarsG76]

What was the "removed word" haha

[riklaunim]

I found that this happens with my Skyris 618C. Perhaps it happens with the OSC camera Bauer due to the color pixels not being aligned perfectly...

Nope, that's atmospheric dispersion and is visible for any camera or eyepiece. Blue wavelengths shift much more than red so the image gets split. Mono cameras can refocus between filters, while color cameras can't. There are however atmospheric dispersion correctors allowing perfect focus imaging of low altitude objects.

[Ruud]

Yes, atmospheric dispersion. You can repair it in photoshop with the nudge tool on the colour channels. Just use the arrow keys to nudge the blue and red channels a few pixels.

[lrt75914]

Nope, that's atmospheric dispersion and is visible for any camera or eyepiece. Blue wavelengths shift much more than red so the image gets split. Mono cameras can refocus between filters, while color cameras can't. There are however atmospheric dispersion correctors allowing perfect focus imaging of low altitude objects.

I feel really stupid now, because I should have known that it could have something to do with the way the atmosphere refracts light. I'll just chalk that up to sleep deprivation .

What was the "removed word" haha

That would be p'ss XD.

[MarsG76]

Nope, that's atmospheric dispersion and is visible for any camera or eyepiece. Blue wavelengths shift much more than red so the image gets split. Mono cameras can refocus between filters, while color cameras can't. There are however atmospheric dispersion correctors allowing perfect focus imaging of low altitude objects.

I see.. thanks for the info, I always though it was a limitation of the OSC sensor... it still it can be fixed by re aligning the R & B channels to G.

[MarsG76]

I feel really stupid now, because I should have known that it could have something to do with the way the atmosphere refracts light. I'll just chalk that up to sleep deprivation .

That would be p'ss XD.

ha ha.. tops