How to collimate a Dob with a laser collimator.

[StargazerMan (Frank)]

When I was starting out, I thought collimation was this really super-complex thing. Then when one of our astronomy club members showed me physically with their scope how to do it, I was surprised at just how simple it was!

So I made a video as a basic guide for laser collimating a reflector,
(in this case a 16'' GSO Dobsonian with a Kendrick laser collimator).

Obviously there's a lot involved in collimating and this video is not attempting to cover all those facets. It's intended as a quick explanation of the principle. I found that seeing the basics explained in simple terms without complication was key for me to then use that as a base to learn more.

For beginners, there's a fine line between giving enough info to do the process correctly versus information overload.

Once you get the basics down, it becomes clear over time the different areas that affect the outcome such as mirror springs, focuser slop, mirror quality, laser misalignment... the list goes on, they all certainly need to be understood but only by getting started and doing can you really learn.

[Startrek (Martin)]

Hi Frank,
The only problem with relying on just a laser collimator to collimate ,you have to ensure that instrument is accurately collimated itself.
I use 2 instruments, a Cheshire eye piece and a laser collimator to collimate my 12” f5 dob, 8” f5 imaging newt and 6” f6 imaging newt.
I made up a V block to test my collimator against a wall 4m away inside the house by rotating it 360degrees both ways and ensuring the red laser dot remains stationary.
I have found the Cheshire in most cases has been more accurate than the laser collimator. Hence one instrument checks the other.
For observing super accurate Collimation is not so critical but for imaging it does make a huge difference to your Star shapes in your images.
Cheers
Martin

[StargazerMan (Frank)]

Hi Martin. Wholeheartedly agree with all of that!
I started off using a Cheshire EP alone (on a home made 12'' Newt) and 'Frustrating' is a polite term for the time spent collimating it. :-P
Sound advice that the Cheshire alone can be a better indicator of collimation though I've found that showing newcomers the laser method, they seem to catch on to the whole process faster as the visual aspect of it is more intuitive (IMHO). I think for visual observing as you say, getting it fairly good is good enough and over time you begin to demand more form the gear and you begin paying much more attention to collimation (and all the other little things that collectively add up to affect the views).

I agree that you do need to check the laser itself and that home made 'v' jig is great for checking. I found that the next biggest issues were focuser and mirror slop.
I think I may make a V2 of this video to explain these (again in laymans terms).

[OzEclipse (Joe Cali)]

Martin's method will work very well however providing the focuser is a good fit, ie the laser collimator doesn't rattle in the focuser tube, you can test it quickly and easily by rotating the laser and watching the spot on the mirror. Scope doesn't need to be collimated.

Joe