Idiot's guide to collimation?

[the lemming]

Hello

While researching what telescope to buy, which I have now made my mind up on I learnt a new word which has now struck fear in to my tiny little mind.

And that word is collimation.

Any chance of somebody explaining how to do this or posting a link or two on how to do this would be most appreciated.

Also, is it possible to do without buying an expensive lazer, or are they essential?

I'm guessing that they weren't around a few hundred years ago when Newtonian telescopes were first used.

Cheers

[sixela]

A collimation eyepiece, which is a combination of a Cheshire eyepiece (invented by professor F.J. Cheshire, described in publications in 1920) and a sight tube. More reliable than a cheap laser collimator.

In a nutshell:

1) You fix the placement and rotation of the secondary (that's mechanically tricky on some scopes) so that it appears centred and round under the focuser; you use the sight tube's far inner edge as a reference for that. The tricky bit is that the secondary itself (not to be confused with the silhouette reflection of the secondary in the primary's reflection) is often hard to see, unless you e.g. place a piece of coloured paper on the opposite tube side from the focuser or between the secondary and primary.

2) You then aim the reflected focuser axis to the centre of the primary (you set the tilt of the secondary so that the centre spot appears under the sight tube's cross hairs.)

3) You then aim the reflected focuser axis back at you by tilting the primary. The visual cue is that then, the primary reflection and the reflection of the Cheshire ring are concentric.

The most important thing, though is to ignore other things like spider vanes or the silhouette reflection of the secondary (which for reasons of perspective will not be concentric with the rest!)

The second most important thing is to know that 1) is harder than 2) which is harder than 3), but that the hardest things are least important (so if you don't get 1) perfectly nailed, it's OK to give up and proceed to 2) and 3), leaving 1) for another attempt).

The third important thing to know (when iterating a couple of times between 1) and 2) and getting frustrated) is that once the secondary is well placed, you're not likely to have to tweak placement again until you disassemble the scope.

[John]

Try this - written by one of our members:

Astro Babys Guide to Collimation

Laser collimators can be more trouble than they are worth.

[Astro_Baby]

Collimation - probably the second most frequesntly asked question on forums (the firts being 'what telescope should I buy' and the third being 'how do I polar align' )

It can be scary for the beginner but it actually not that hard. A bit of patience, some time and its done.

The first time you do it you will curse, swear, threaten to throw the telescope through a window possibly. The second time it will be easier and after that you'll wonder why it ever seemed difficult.

Just be sure that the firtst time you do it you have plenty of time spare.

[NickMilner]

Another vote for Astro Baby's article, as a newbie (and all her other articles!)

[sixela]

Or try to get someone more experienced show it to you once. It's hard to explain but easy to do (a bit like tying shoelaces), and if someone else shows you how to do it, you'll wonder what all the fuss is about.

[Carbon Brush]

Another positive on learning collimation.

First time, big worry.

Second time. Need to concentrate.

Third time, no problem.

If you get really bothered, then I'm sure someone at a local astro soc, or a local SGL member would help out.

[rowan46]

this may also help. astro baby's tutorial is wonderful but some people like to be shown

Collimating a Newtonian

[the lemming]

Thanks for the replies as it is much appreciated.

Cheers

[russ]

Good luck with your first collimation.