Query re. weird colour defects when observing Jupiter

[wolfpaw]

Hi

When looking at Jupiter I notice some strange colour effects. The right side of the planet has a sort of blu-ish crescent at the far edge. The left side has the same effect but the colour is a sort of reddish/orange. I wonder if this is an issue with the eyepieces or the telescope itself, or whether it's just an artifact from the seeing conditions.  It's particularly noticeable when I barlow my 16mm EP.

I guess it looks a little like this photo I found online:

Anyone know what causes it?

Thanks!

[Tiny Small]

That is chromatic aberration (unless it's some odd atmospheric refraction from the planet its self but I doubt it). Lots of optical equipment suffer with it to one degree or another. The likely culprit here is the eyepiece and your 250p is unlikely to be at fault. It can be caused by poor or worn lens coatings, incorrectly aligned lens elements, bad refraction qualities of the types of glass used etc. Some types of camera lens (and I assume therefore eyepieces) are just prone to this behaviour under certain lighting conditions and have to be lived with or replaced, but if it is due to the type of lens/EP, then replacing it with  like is unlikely to solve the problem.

Did it ruin your views or is it just something you noticed? If it's the latter, I wouldn't worry about it. If you feel it's spoiling your views, get a different EP.

[AndyWB]

... (unless it's some odd atmospheric refraction from the planet its self but I doubt it). 

I saw this when I was out last, but it seemed to come and go with the seeing. I did put it down to the atmosphere - but I could be wrong...

Certainly, I've always seen this looking at Venus, though being much lower, there's much more atmosphere.

[wolfpaw]

That is chromatic aberration (unless it's some odd atmospheric refraction from the planet its self but I doubt it). Lots of optical equipment suffer with it to one degree or another. The likely culprit here is the eyepiece and your 250p is unlikely to be at fault. It can be caused by poor or worn lens coatings, incorrectly aligned lens elements, bad refraction qualities of the types of glass used etc. Some types of camera lens (and I assume therefore eyepieces) are just prone to this behaviour under certain lighting conditions and have to be lived with or replaced, but if it is due to the type of lens/EP, then replacing it with  like is unlikely to solve the problem.

Did it ruin your views or is it just something you noticed? If it's the latter, I wouldn't worry about it. If you feel it's spoiling your views, get a different EP.

Thanks for the reply.

No, it didn't ruin the view as such. I noticed it and found it a bit annoying. I'm a bit obsessive about little things that crop up and worry that it's an error with the telescope or that it's not working as it should.

Do reflectors get chromatic abberation? If it's the EP then I think it could be the barlow lens, a Baader Q-Turret. I've got some Maxvision EPs which I would hope aren't subject to chromatic abberation.

[wolfpaw]

I saw this when I was out last, but it seemed to come and go with the seeing. I did put it down to the atmosphere - but I could be wrong...

Certainly, I've always seen this looking at Venus, though being much lower, there's much more atmosphere.

I saw it with Jupiter last night. The seeing didn't seem that great and there was a lot of moisture in the atmosphere.

[wolfpaw]

Found another discussion about the same phenomenon:

http://cs.astronomy.com/asy/equipment/f/9/t/25683.aspx

Seems it could be the atmosphere, but Jupiter was really high last night although it was very bright.

[Moonshane]

This sort of effect is most common with the atmosphere where the planet is low in the sky. as it rises the effect disappears although at that stage you may find CA within the eyepiece of course or the scope depending on the system used. better quality eyepieces (or a different system) will correct the latter but only space travel or waiting a bit will correct the former.

[wolfpaw]

This sort of effect is most common with the atmosphere where the planet is low in the sky. as it rises the effect disappears although at that stage you may find CA within the eyepiece of course or the scope depending on the system used. better quality eyepieces (or a different system) will correct the latter but only space travel or waiting a bit will correct the former.

My 250PX wouldn't, in itself, be responsible though?

[Uranium235]

My 250PX wouldn't, in itself, be responsible though?

Impossible. As red, green and blue all come to focus at the same point with a reflector. As mentioned before, the culprit is most likely a poor EP or really poor atmospheric conditions.

[Moonshane]

sorry, yes I meant if you have a system that creates CA (broadly most refractors). your system / scope being a newt would not.

[wolfpaw]

Would it be related to the fast speed of the telescope? Would it be less noticeable with the same EPs in a slower scope? (it's not distractingly noticeable at the moment. Last night it was just definitely there with Jupiter. I can't remember if I've seen it before it not!)

[astromerlin]

It's refraction of the light wavelengths through earth's atmosphere, I have always had this when planetary imaging through my reflector to some extent more or less. The worse the seeing conditions the more pronounced it is, I would hazard a guess that seeing it through an EP meant that the seeing was poor (could have been looking though the jet stream?) a slower f ratio scope it would be less dramatic.

[Tiny Small]

CA is usually caused by poor optics, but even great optics can suffer with it if the lighting is bad (photographically speaking). Astronomically speaking, this relates to poor seeing with lots of moisture in the air as pointed out above. It is caused when light entering the optic is bounced around at angles too great for the optic to deal with which then causes the light to refract inside the optic. Bad seeing conditions can cause the light to refract (to a degree) before it even enters the optic.

My advice; don't worry about it.

[Moonshane]

affecting the atmosphere is not something that's possible other than as I said earlier by travelling above it.

the type of scope would not affect this.

in this case, that's what I think it is

[wolfpaw]

Thanks for all of the replies. It's reassuring that others have noticed it sometimes too. When you're first starting out it's difficult to tell what's normal and what isn't. There was a lot of moisture in the air last night as fog had been forecast and before I came inside I could see a steadily increasing halo around the brightest stars (and Jupiter). We'd had a lot of rain earlier in the day too.