Collimation... does my scope need it or is this normal?

[matsey]

I have very purposefully steered clear of collimation since I got my scope a few months ago, to be honest I think like lots of other newbies, the idea of trying terrifies me !!

I do have an SCT scope, which I (think) shouldn't need collimating often in the same way as other scope types do, but I can't work out if it needs it now.

When I defocus a star and the star is in the very centre of the eyepiece, everything looks fine and circular, exactly like the images I've seen of a correctly collimated scope. However, when the star starts drifting out of centre, I do start to notice that the white lines "flatten" on one side slightly so the defocused star is no longer completely circular at the edge. It definitely seems to get worse the closer to the edge of my FOV it gets.

So, is that normal? I hope so, but I've really no idea.

When the stars are in focus however stars at the edge of the field look as sharp as the ones in the centre (at least in my 24mm TV Panoptic they do ). But as this is my first scope, although what I'm viewing looks just fine and I don't think I'm having focusing problems, I'm not sure I'd be able to tell, perhaps having never seen it corrected if is in need of collimating.

Thanks all

Matsey

[John]

You need to put a star in the centre of the field of view (Polaris is good) and de-focus it so it forms a small disk of light with a dark circular shadow in the centre. If the circular shadow is right in the centre of the de-focussed star disk then the scope is in good collimation. If the shadow is offset then the collimation needs adjusting.

A cooled scope helps with this.

[rwilkey]

Have a look at Astrobaby's definitive guide: Astro Babys Guide to Collimation

[Demonperformer]

Just a thought ... when I started enquiring about collimation on my 6SE, I took an image of the star with my webcam and put it on SGL and got some really helpful comments: http://stargazerslounge.com/equipment-help/90785-do-i-need.html. If you still have problems after checking out AB's guide, it might be worth doing something similar.

[NGC 1502]

When I defocus a star and the star is in the very centre of the eyepiece, everything looks fine and circular, exactly like the images I've seen of a correctly collimated scope. However, when the star starts drifting out of centre, I do start to notice that the white lines "flatten" on one side slightly so the defocused star is no longer completely circular at the edge. It definitely seems to get worse the closer to the edge of my FOV it gets.

So, is that normal? I hope so, but I've really no idea.

Hi Matsey, what you describe is a well collimated scope, so I'd leave it as it is

Regards, Ed.

[matsey]

Hi everyone, thanks as always for all the responses. It is definitely OK when the de-focused star is in the centre of my FOV, so it sounds then that my collimation is all good. Phew!

Thanks also for the links, they're really good reads, and I have bookmarked them (in my ever-growing Astro links folder!), so if/when it does look like collimation may be required, I can go back to them then... fingers crossed though that won't be for some time yet