Got my collimator...ummm...hmmm

[kljucd1]

Hi,

I finally received my new laser collimator and I seem to be having a problem with it, I think.

First let me say that I tried a visual collimation about 1 week ago and was able to see the best image of the moon I have seen since buying the scope. Then I went to Kangaroo Valley and saw an absolutely amazing view of M42. However, I figure that collimation isn't a particularly interesting thing to have to do, so I bought a laser collimator.

After following the instructions on Andy's Shotglass (http://andysshotglass.com/Collimating.html), then I end up with what can be see in Pictures 1, 2 and 3. I tried to get it to line up, but each attempt would improve one part of the optical line, but did nothing for the rest of the scope.

After getting pretty annoyed with it, and as there was a few holes in the clouds last night, I decided to try again but by collimating it while pointed at the moon.

Anyway, I pointed it at the moon and did not bother collimating it any further, Picture 4 is the reason why I didn't bother.

So my question is, has anyone come across this before, and how can I fix it. I might be a noob, but I am pretty sure that laser is NOT meant to be coming out the front of the scope.

Anyway, let me know if you have any ideas.

Thanks in advanced

Daniel...

[Starkler]

Step one would be to adjust the secondary tilt to aim the laser dot at the centre of the primary.

Step two is adjust the primary mirror to send the reflected laser dot back to the collimator.

[joshman]

it could actually be the collimator itself, i was in at sirius optics the other week sussing out one for a mate of mine, and ron was telling me that some collimators actually need 'collimating' themselves, to make sure that they do infact point directly down the centre of the tube.

i dunno weather or not your collimator has this 'necessity, but it could be worth looking into.

[davewaldo]

Hi Daniel,

Basically the process for using a laser collimator is:

Insert collimator into the focuser and turn it on. Being careful not to get the laser in you eye, adjust the secondary mirror screws until the laser is in the middle of you primary mirror. Now adjust the primary mirror knobs to make the laser return back up the scope, off the secondary mirror and back into the hole where the laser comes from inside the collimator (some have targets around this hole to help). The last part is the trickiest part.

Once this is done you "should" have a well collimated scope. But unfortunately there are many variable such as; is the collimator collimated, and is your focuser centred....

But this process will get you much closer than you are now.

Hope that helps. :)

Dave.

[davewaldo]

To roughly test if your collimator needs collimating, rotate it in the focuser and see if the beam/dot moves in a small circle. If it does move in a circle bigger than the width of the laser then it needs collimating.

An article about this can be found on this site.

:)

[kljucd1]

Hi,

Thanks for the quick responses guys, very much appreciated.

I had another go, keeping your advice in mind, and all of a sudden it works (I don't know, must have been a dizzy moment or something.) I have put the laser right in the centre of the little window thingymabob on the collimator (which of course means that the laser ain't coming out the front anymore).

So I will have to wait for a few more holes in the clouds to test it :).

But tell me, how come I was able to take some shots of the moon that are pretty good? If the collimation was that far out then shouldn't the image have been totally blurry or something?

Thanks again

Daniel...

[multiweb]

Hi Daniel, I'm a noob too and I had the exact same problem. Here's how I do mine if it helps.

I first take everything off the focuser and stick a white piece of paper in the tube so I can see the secondary against the white background. I then move the secondary with the spider and the various screws until I get it centered in the focuser (roughly a black circle [mirror] against a white circle [white paper in the background]).

Once I'm happy with the secondary it's 99% there. All you have to do is stick the laser collimator in the focuser and make sure the laser points directly in the center of the primary.

When this is done, tweak the primary until the laser goes back and center it in the focuser. That's all. Rotate the collimator in the eyepiece as well and check the laser still points in the center of the primary.

To check if your collimation is good point to a bright star and go out of focus slightly. You'll see a black hole in the star. If it's centered, you're all good. If it's offset then you're out.

[Roger Davis]

Lasers do not tell you about rotation of the secondary, nor does it tell you if the secondary is properly aligned under the focuser.
First step in collimation is to square on your focuser to the mechanical and optical axis before you tinker with anything else.
You will need a Cheshire to properly centre the secondary and eliminate any rotational errors. Then use your laser to finish off the rough collimation. Final collimation should be done on a star.

[vash]

The moon probably won't come out too blurry from bad collimation, If you take a shot of a star field you'll find that the stars on the outside are shaped like tennis rackets.

Collimating a scope just makes all the light it gathers bounce back into the right spot, but even if it's out your still going to get some light in.

[kljucd1]

Hi Guys,

Thanks for the info, I am going to test once I get some clear sky. I am interested to see if I get what you descibe Vash.

Thanks

Daniel...