about coma...

[jamieren]

I've noticed when observing stars through my newtonian that there is a slight "smear" to the image, red on one side and blue on the other. It's hardly noticeable at 60x but at higher powers is more evident. Is this caused by the parabolic (primary) mirror or does it have something to do with eyepieces? Would a paracorr correct this?

[Astronut]

Is it noticable on axis or just towards the edge of the FOV? Coma is more evident towards the edge of the FOV and it doesn't have false colour associated with it so I suspect the chromatic aberration is from the eyepiece.

[Andrew*]

Jamie,

I had this observing the moon the other day. My eye was not perfectly central on the exit pupil, so I was looking at the lenses from an angle. This meant the eyepiece was acting like a prism and splitting up the light into orange-yellow on one side of the FOV and dark-light blue on the other.

Does this sound like your problem? If so, just keep your eye central and it shoudl go away. It would not be connected with coma.

Out of interest, which eyepiece did you use?

Andrew

[jamieren]

I was using the 32mm GSO plossl which it was less noticeable in (barely at all) and my speers-WALER 10mm (more noticeable). I'm supposing it was less noticeable because the mag is 1/3 in the 32 what it is in the 10mm. I've got a 14mm pentax xw on the way (finally made a decision!), we'll see what that one does. It happened on axis as well as off axis (though off axis it was more prevalent, of course). I am probably just naive, but I've never intentionally observed "coma" in my scope. I'll admit though that I tend to keep things near the center of the field of view, though.

On another note, I've got a guy willing to sell me a 24mm panoptic (like new, he says) for $260 cdn. shipped. I've read it's the largest fov available in a 1.25" eyepiece. New they currently sell for around $350 cdn. + tax & shipping. Sound like a good deal? Also, there's another (unrelated) 7mm nagler for $220 shipped and I'm having trouble deciding which to go with. The 7 is cheaper and I'm interested in higher mag especially, but I'd get more use out of the 24 (then the 32 plossl would likely become obsolete...).

[Kaptain Klevtsov]

If it happens when looking at low down things, then its due to the atmosphere, not the 'scope. Jupiter does this at the moment, but when its higher it looks fine.

Newts don't do colour fringes.

Kaptain Klevtsov

[John]

On another note, I've got a guy willing to sell me a 24mm panoptic (like new, he says) for $260 cdn. shipped. I've read it's the largest fov available in a 1.25" eyepiece. New they currently sell for around $350 cdn. + tax & shipping. Sound like a good deal? Also, there's another (unrelated) 7mm nagler for $220 shipped and I'm having trouble deciding which to go with. The 7 is cheaper and I'm interested in higher mag especially, but I'd get more use out of the 24 (then the 32 plossl would likely become obsolete...).

The 24mm Panoptics don't come up very often and are superb - it would replace your 32mm plossl as i) it shows the same amount of sky and ii) the extra magnification darkens the background sky a little making faint objects a little more easy to pick out.

On the 7mm Nagler, it depends which type it is - that seems a lot of cash for one of the older type 1's but about right for a type 6 which are superior IMHO. Ask which type it is. It would be useful in your scope on good nights but 7mm Naglers do come up a little more often than 24 Pans do so I'd go for the Pan if I was in your shoes.

John

[FLO]

If it happens when looking at low down things, then its due to the atmosphere, not the 'scope. Jupiter does this at the moment, but when its higher it looks fine.

Newts don't do colour fringes.

KK has nailed it. When the object is low to the horizon the moisture in the air acts as a prism. If you look at an overhead object I doubt you will see the same effect.

[jamieren]

If it happens when looking at low down things, then its due to the atmosphere, not the 'scope. Jupiter does this at the moment, but when its higher it looks fine.

Newts don't do colour fringes.

Kaptain Klevtsov

Thanks guys, I'll keep it in mind.