LightBridge Collimation Problems / Chromatic Aberration???

[shredder]

Hi All,

I haven’t had the scope out for a while now, time just seemed to always get away from me....

But last night it made a comeback, and so out it came. A nice new Meade LightBridge 12” (ok so its about 1-2 years old but rarely used).

Anyway after using it for a while I noticed a few things that I wanted to check up with someone who knows.... While I have had this scope for a while I haven’t really used it in anger, or for any long duration until last night.
What I noticed was what looked like Chromatic Aberration. Now I wasn’t expecting this as the scope has no lenses, so either I was mistaken, and this was due to some collimation error, or this is occurring via the eyepieces.

To assist with this discussion...

The scope had been out for some hours before hand so was as cool as it was going to get. I had collimated the scope with a laser collimator several times (to ensure it was consistent). And the eyepieces I was using were all Meade 4000 UWAs or SWAs (6.7mm UWA, 8.8mm UWA 13.8mm SWA, 18mm SWA, 24.8mm SWA). Oh and the target was Jupiter.

What I was seeing was on Jupiter, a purple fringe on one side, and I think an orange tinge on the opposite side (could be wrong there). The effect seemed to be in one axis only, kind of like the scope wasn’t coming into focus properly in one axis. And this was with the object in the center of the FOV.

So is this chromatic aberration caused by the eyepieces? I am a little surprised as these are supposed to be good eyepieces. Or is this caused by some collimation issue with the scope its self? Do I have to be more accurate with the collimation?

But more importantly, is there anything I can do to fix the problem? I suspect I might be a little lax with my collimation, even though I did do it several times, but even so I also recall seeing this effect before. I also noted that with a cheaper Erffel and Plossl that this effect was not visible... hence this leads me to suspect the eyepieces... is there a problem with the UWA/SWA in an F5 scope...

As you can see I am babbling now....

Thanks

M

[astronut (John)]

Hi M,
As long as your collimation is accurate, this is important in any scope especially anything F5 and below.
The E/P's that you're using sound like the culprits.
These are more suited to scopes with F stops of 6 and above.
If you are able to use another set of good quality e/p's you will see a difference.
BTW where are you situated?

Cheers, John.

[shredder]

Thanks John,

The collimation is as good as I can get it. Maybe not perfect, but it must be pretty close. I find the mirror in the 12" is very heavy and so causes some movement (even with the replaced springs) so I check the collimation throughout the night just in case its shifted...

I was wondering if it was the speed of the scope causing this effect. I bought these EPs when I had a SCT, and with a F stop of 10 they worked a treat. So I collected a fairly complete set, especially as a wide FOV is an advantage on a SCT. When I sold the SCT I decided to keep the EPs as they were/are a good quality set...

Now I have a nice fast scope, and all my good eps are no longer suitable!!! Brings you to tears.... especially when my fallback position in EPs is not so good.

BTW I am located in Sydney.

Thanks for the help.

Michael