focusing help

[joe_coke]

So i'm looking at saturn last night and i have it dead center and switch to my x2 barlow and 10mm eyepiece. The planet gets a little bigger (still can't make out any detail) but when i bring it into focus, i get three ghost saturns splitting off in 3 directions. Pull the focus out and i get the classic blurred airy disc. Could the eyepiece just be pants or is this what happens when trying to focus througfh a barlow?

[rwilkey]

Hi there, what telescope do you have? Focal length and aperture would be helpful...

Edit: Just read your signature, sorry!

[rwilkey]

The Barlow and the 10mm ep are not the best quality/combination. Better without the Barlow I should think.

[joe_coke]

Ok thanks for the advice, what i was suspecting it was. I think i'll get a 6mm plossl and see if that can give me the magnification i'm after, if not then i've got the wrong scope and i'll start researching again.

thanks.

[umadog]

I don't know why you see three ghost images. That's very odd. What you haven't seen, however, is an airy disk. The airy disk is what you see when you're at focus on a star (not a planet). Airy disk - Wikipedia, the free encyclopedia It represents the telescope's resolution limit. You will only see it at high powers on a very, very, still night. Personally, I've never had seeing good enough for that.

When you de-focus a little on a star you will see what is effectively an out of focus airy disk. It will look more or less like this: http://www.willbell.com/tm/IMAGES/StarTest2.jpg You won't see that on a planet either, because a planet is not a point source of light.

If you defocus even more on a bright object then you will eventually see a homogenous disk with the shadow of the secondary mirror and the spider superimposed.

Your telescope is fine: you don't need to go hunting for a new one just yet. All telescopes are limited in what they can magnify by the turbulence in the atmosphere. On most nights this is about 200x. It doesn't matter if you have a 6" or a 16". Neither will get past 200x unless the atmosphere allows. Seeing detail on planets takes two things: a well aligned and cooled-down telescope, and also patience and experience. Spend some time with your scope, get to know it, and spend time at the eyepiece. Then you'll see more.

[joe_coke]

Thanks for the education! i learn something everytime i visit these forums.

The ghosts seem to be as if the spectrum is being split three ways, i'll try and take a picture...when the sky clears.

thanks for the info.

[rwilkey]

Could be the anti-reflection coatings in either the ep, or more probably the barlow you were using...

[umadog]

Ah... I've seen diffraction spikes cause chromatic aberration on planets. This is a long shot, but are your spider vanes tilted? They should be parallel with the incoming rays so as to minimise their cross-sectional area as viewed from the primary. If they're twisted you'll get terrible diffraction. It's possible that this, along with something else, was responsible for what you saw.

[pel]

I'd make sure your scope is collimated correctly.

The SW barlow and 10mm have a bad rep, but they aren't that bad.

I like this collimating tutorial, if you need help with that -

Collimating a Newtonian

[joe_coke]

I did have my first go at collimating (i bought a cheshire with my scope after all the threads on here suggesting so) and i thought i had it well setup. I will take a look at it though, being my first go it may be rubbish.

cheers folks.

[jflowers]

The only times I have seen ghost images around a planet was

1. when viewing through a double glazed window

2. when it wasn't cooled and out of collimation