Two Collimators two results- what the?

[glend]

I have two laser collimators, one which I bought (GSO) and one borrowed (Prostar), and of course when placed in my scope they are nowhere near agreement. The GSO one seems to be better quality and fits the GSO dob focuser better, and is close to alignment. The Prostar is loose in the focuser, regardless whether using at 1.25 or 2" fitting with adaptor. What to do, which one to trust? My gut feel is the GSO is close. Can I confirm them somehow?

[DavidU]

Spin both of them in the focuser and see which one keeps the beam on the primary dot best.

[glend]

Well I decided the GSO was the better of the two collimators (because it held a tighter circle when turned in the focuser), and went through the steps in Mental's thread on collimation of the GSO Collimator:

http://www.iceinspace.com.au/forum/showthread.php?t=75601

I setup and leveled the cross-nail jig 5.5 metres from the target and found it was pretty close and needing just a little tweaking of the adjustment screws to get them all within a 10-12 mm circle grouping. So my question now is how close is close enough? I don't want to get obsessive about it and I think I am at the limits of the jig's and collimator adjustment screw capability to get it closer at that distance.

In the scope it looks great, once I get that pesky laser dot onto the mirror centre donut (using the lock screws of the focuser and abit of tape on the collimator shaft) and tweaked the primary adjusters a little to centre the return dot in the collimator window. It was close already, but I'd expect that with this relatively new scope.

Now how often does it need to be checked? I have to move the scope each time I use it (on my customised hand truck), and it's been up and down the yard many times now but was pretty darn close to perfect when I checked it.

[mental4astro]

At home, I check the collimation every third or forth session. I'm not obsessive about it, but I wouldn't let it go past four - you will notice the difference. But this also depends on your scope. All my Newtonians use heavy/strong compression springs and not locking screws. This means I need to check the collimation a little more readily. If my scopes are subjected to any jarring or knocks, I just check it - just takes a minute.

Another thing, the collimation process is not a tedious one. It really isn't. Once you've got the hang of it, and understand the process, you will find yourself insisting on doing it, knowing that the minute or two that it takes makes a huge difference in the image quality you will get.

How tight a circle grouping should you aim for when tweaking the collimator - as bloody good as you can get it! While the frequency of collimating the scope I'm not obsessive about, making sure the collimator is spot on I am. Yeah it's a pain in the backside, but its just the thing to do when the full Moon is up, or when it's raining, or when you should be mowing the lawn, or cleaning out the car, etc. These are those little things that we amateurs can actually do to get our gear working to their optimum. The results are really worth it. Honest! :)

[Logieberra]

I came across a really great vid on laser colllimator collimation on YouTube by Astronomy Shed.

https://www.youtube.com/watch?v=bE09_X43UUQ&feature=youtube_gdata_player