Seeing red .... and blue

neB · #1 31-01-2007, 01:55 PM

I'm getting blue and red edges on most stuff I'm looking at. Not the moon, but everything else from Saturn and Jupiter down in size.

Red on one side, blue the other. This just smacks of refraction, but what's causing it??

I thought it was a collimation issue, but I've checked and re-collimated a few times and I think that's OK.

Can anyone shed some (non-diffracted) light on this for me please?

Thanks,
neB

[1ponders] (Paul) · #2 31-01-2007, 02:02 PM

It sounds like chromatic aberation. But with a reflector you aren't supposed to get that. Are you using a barlow? And what sort of eyepieces are you using? Also how close to the horizon are you viewing? Does this happen at all altitudes or only low to the horizon?

janoskiss (Steve H) · #3 31-01-2007, 02:13 PM

Combination of miscollimated scope and dispersion in the lenses in eyepiece will give you false colour. If the scope is collimated properly you should not see false colour on axis (in the centre of the field of view) even with cheap eyepieces. But if your target is low in the sky the atmosphere alone will show chromatic aberration.

neB · #4 31-01-2007, 02:26 PM

It's happening at all altitudes. Last night I was looking at Orion - pretty high in the sky.

I was using a Barlow, but this was happening before I bought the barlow.

Eyepiece, last night, was the 25mm that came with my Saxon - ie: a cheapie.

Only had a quick look to see if the re-collimation attempt on Sunday had done anything. I'll run some more thorough tests when I get time and report back.

Anything specific I could look out for?

Thanks folks.