Another rambling post from me, but I wanted to share some thoughts with you about collimation.
I get the feeling that most people don't realise how critical collimation is - and (like myself) they tend to collimate their scope to the limit of the tools they have on hand and not go the final step with a high-power star test.
If you haven't already read this article, I highly reccommend that you read Thierry Legaults page on collimation:
http://www.astrosurf.com/legault/collim.html
Just to repeat myself, I think that when most people say their scope is "collimated" what they actually mean is that it looks as good as it can be with their collimation tools.
But there is a world of difference between "close to collimated" and "perfectly collimated". It's easy to get close, and a real test of patience and skill to get "perfect".
So why not stop at "close" to collimation? The answer is clear if you've read that article linked to above - you can still be losing *half* of your resolution if you stop at the limit of your tools. All it takes is for the diffraction rings in the airy disc to overlap a little and you're done for.
The real test of collimation is to look at a not-too-bright star, say mag 2, at ludicrous magnification of say 100x per inch of aperture. If the rings don't look circular then you're not finished collimating.
Practical point - last night I spent my usual ten minutes or so getting the collimation "spot on" according to my tools, and yet when I checked a star this morning just before I started imaging the collimation looked hopeless. I was wishing that I had an extra hour before sunrise to tinker with it and see if I could get it a bit closer to correct.
The tools I use for collimation (barlowed laser, autocollimator, cheshire) can get me very close to collimated, but it was very obvious from the high power view later on that I wasn't really that close after all.
Like so many other parts of this hobby, collimation is somethig that we should all keep working at to improve. It's no secret that one of the skills that sets Damian Peach apart from most others is his insistence of perfect collimation before he starts imaging.
Collimating a scope isn't hard in the way that, say, brain surgery is hard - all it takes is a lot of patience and persistence.
regards, Bird