Collimating 10 in. Dob

Good Afternoon everyone:
Well I made my first attempt at collimating my 10 inch dob over the weekend. What a disaster! I moved the diagonal, I moved the primary; Heck I moved everything! But try as I may I couldn't get the laser spot in the center of the primary and still have the returning spot line up with the hole in the eyepiece. Is this process as hard as it seems or am I doing something wrong? Here is the question: Should I be able to get the laser spot in the center of the primary and at the same time have the return beam plumb in the center of the eyepiece hole. I can get the spot in the center of the primary but then it isn't in the center of the eyepiece hole and when I have it centered in the eyepiece hole the spot on the primary is only halfway to the center of the mirror (one third from edge) Any advice will be graciously accepted!

1. First center the laser on the primary by adjusting the "secondary".

2. Then center the laser back to the eyepiece by adjusting the "primary".



Mark Visser

I've had similar problems. I noticed that if the eyepiece holder has a set screw, and the collimator is the tiniest bit loose in the focuser, then tightening the set screw to tighten it can actually tilt the collimator a tiny bit, and affect the laser path a considerable amount. In order to make sure the laser was really shooting straight, I would try setting the telescope perfectly horizontal with the focuser pointing straight up. Then rest the laser in the focuser with out tightening and see where how goes. It worked for me.

Philip,

I am not experienced enough to help with your laser collimation problem. But I wanted to share with everyone a video that a right nice fellow put together on how to collimate with a collimation cap. It provides some most excellent gouge and even better animation on what things should look like. I apologize for not answering your specific question, but this site has some great tutorials for us new guys.

http://www.andysshotglass.com/Collimating.html

Clear skies,

Tom

Actually, I just went and viewed the video again and it has some laser gouge.

Philip,

That video didn't mention squaring the focuser and that is an excellent point brought up by other folks.

If you have a 4 vane XT10(i), I have found a quick and easy way to check your focuser for square:

http://www.tomhole.com/Focuser.htm

It's at the bottom of the page.

Clear skies,

Tom

Philip,

I can't disagree with anything said. I would add most of this is probably overkill. Mark hit the nail on the head right out of the box.

First collimate the secondary - use the laser, adjust the secondary until the beam is in the center of the primary (hopefully it is center dotted).

Then collimate the primary by adjusting until the beams match up (or you hit the hole).

If you've got them way out you may need to rough collimate. Also if way out, you may notice your secondary is no longer putting the laser in the middle after you adjusted your primary. Just go though the loop again and it should be fine.

The first time or two is nerve racking, but once you do it about 3 times it becomes a 2 minute job. I can do mine in the dark while talking to someone.


Ed