Ray, ta for the thumbs up on the little write up of mine on collimating lasers. My understanding on the collimation process has grown since writing that article, and it may be time to add to it.
What needs to be also mentioned is lasers DO NOT totally collimate secondary finders. Secondary mirrors also have twist, vertical and lateral factors relative to the focuser that need to be looked at that a laser will not deal with.
Vertical and lateral factors are not as critical, as once the twist factor of the mirror is dealt with, these two other factors will determine just how much light is actually getting to the eyepiece. Optimal vertical and lateral position of the secondary will maximise the amount to light getting to the eyepiece. But give a secondary mirror a nice twist out of alignment (only needs to be a small amount), and you will still get the secondary and primary mirrors to 'collimate', but a simple star test will show you they are not.
Getting my head around this has been the hardest things to learn about the collimation process. The idea of collimation is a simple one: align the blasted optics. At first I too thought a laser was the answer. They are not and ONLY help once the secondary mirror is correctly aligned to the focuser.
There was a fantastic animation created by another IIS member that shows how the case can be that the secondary is not correctly positioned to the focuser, but the laser 'shows' that the optics are 'collimated', but buggered if I can find it now...
But, once the secondary is correctly positioned, a laser can be used to deal with the collimation
first of the secondary
and then the primary.
Cheshire eyepieces and its variants will deal with this. They are deceptively simple devices, but man, they will brow bash you senseless until you get it. I have only just come to terms with Cheshire eyepieces in the last few months too. There is a protocol to follow with these, and the real tease comes only from learning what to look at in the line of process and what to ignore until the correct sequence number is up for that factor.
Without going into too much detail right now (I've gotta go soon), the sequence in collimation is:
1: Align the secondary to the focuser. This deals with twist, vertical and lateral positioning of the secondary.
2: Collimate the secondary
3: Collimate the primary.
While the GSO, Bintel and other similar laser collimators are not perfect, they do help. For some people that do not want to spend too many $$$ on this hobby, these gizmos are fine. There are more refined units, but don't forget that a simple Cheshire eyepiece will do the same job, AND will deal with your secondary most effectively.
