collimation?

[northcanadian]

Hi folks:

I was imaging Jupiter and Venus last night...could not quite get good focus. using a 9.25sct. With a 32 mm eyepiece, and racking the focus slightly in and out beyond focus, I noticed what looked like a diamond ring...with a brighter spot about 2 o'clock on the ring itself. Should this be centred, and is it the airy disc?

Thank you again for your help...thought I had the collimation resolved (another senior moment).

Cheers

Roger.

[Freddie]

That may be as a result of thermals in the tube. Had the scope had at least an hour to reach ambient temp?

[northcanadian]

Thanks Freddie...I actually keep the scope outside in a small observatory/shed. I had opened up the roof several hours before attempting to image.

Cheers

roger

[JamesF]

I'd point the scope at a nice bright star, Vega, say, and run it in and out of focus in both directions. Before the image blurs into a pale white disc with a hole in the middle you should see lots of concentric rings. They may be wobbly, but they should be concentric rather than obviously elongated or with the centre pushed to one side. If they are elongated or not nicely concentric then you probably do have a collimation problem.

This is an image from my 127 Mak taken after I'd stripped and rebuilt it and redone the collimation. Obviously it isn't an SCT, but should give you the general idea:

James

[Pete Presland]

very nice collimation James!

[JamesF]

very nice collimation James!

Thank you If I'm being uber-critical I think it's the tiniest amount out, but such a small amount that I'd never be sure I could get it any better. Not unless I had an artificial star to use during the daytime, anyhow. I'm certainly quite pleased with it given that I did it by eye using an eyepiece I'd made by drilling a small hole in the centre of the lid from a five litre plastic container as my only aid

James

[northcanadian]

Thank you gentlemen...I shall give it another try

Cheers