Do I have dodgy optics?

[hobbesy]

I have a Vixen ED81s that I got ex demo from TSO. The rest of the visual train is good too. WO carbon diag and a Baader click zoom 3. Ive also got a baader neodym in there. But when I look at Venus and to a much lesser extent Jupiter at a high-ish mag I get a blue tinge tip right and a red tinge bottom left of the object. This is worse with the rubbish SW Barlow I got with my 130p but still there on Venus without.

Is it just that I'm pushing it for magnification when they're low in the sky and I'm on my not terribly dark balcony in Central London?

Or does that sound like misaligned optics?

When I defocused on Venus the blur was nice and round but there was a circle within circle towards the top right. (Bear in mind that Venus isn't a complete disk tonight.)

Jupiter's moons however were tiny but pin sharp.

What do you guys reckon?

[cathalferris]

Atmospheric dispersion. Natural prismatic effect of looking through a wedge of air, when the target is lower towards the horizon. You'll find that the red edge is vertically down, and the bluish edge is vertically up. Gently nudge the scope tube up and down and see which direction it moves in.

[hobbesy]

Ahh nice one, thanks mate. I thought it probably was, but given I've not got anywhere dark with it yet where i can properly road test her I was a bit worried.

[E621Keith]

As Cathalferris said, it's atmospheric dispersion. The effect get worse near the horizon. There are correctors out there designed to cancel this effect, but they are not cheap

Astro Systems Holland - Atmospheric dispersion corrector

[hobbesy]

Heh. That looks like a nice bit of kit, but there's no way I can justify spending that. I only do visual anyway. Thanks for the ninja-quick replies guys.