How's this one for you? Laser Collimation Problem.

Well the other night I collimated my new LXD75 SN-10. But I had this feeling that I should have had better resolution on M31 even though I was in a light polluted suburb. I was using a UHC filter, I just had this naggin feeling that the collimation was off. I followed the laser instructions I found on-line. I didn't do a star test I know I should have but hear me out.

1. Place the laser in the focuser.
2. Adjust the secondary mirror to center the laser dot on the primary.
3. Then adjust the primary to refocus the laser dot back into the origin hole.

Took no time.

So I was reading up and throughly confusing myself on how to properly collimate this beast being that it has a fast focal ratio f/4 I understand that it's sensitive to collimation being a little off.

So I figured I fire the laser through it again. The dot is centered on the primary mirror but If I rotate the laser collimator 180deg the dot is no longer centered. BLAH.. So I'm not sure what to do. If I line it up this way it will be out of alignment 180deg the other way. I really don't think there is a way to correctly decide. The collimator should always center the dot regardless of rotation correct???

Chris

One thing is that the UHC filter is not good on galaxies like M31. Blocks out too much starlight. The UHC and its cousins the OIII and H-beta filters allow only a few wavelengths through, and are designed for emission nebula that glow only in one or a few colors. (Note the colors mostly appear gray because they are too dim even with filters for our eyes to see the color.) If these filters are used on stars, clusters of stars, and galaxies, then you will lose a lot of light.

Edit: I don't have a laser collimator, but if you rotate the laser and things change as you rotate, the collimator itself needs adjusting. The laser is not lined up with the body of the collimator.

Mike

Chris:

A couple of comments...

1. Collimation will have no effect on the resolution of M31, it is a large diffuse object with no sharp gradients. There is not much to see from an urban backyard. Views of M31 require dark skies.

2. Collimation... I am one cheap dude but I did spend top dollar on a Howie Glatter Collimator and it was a good way to say money. In the 7 years I have had it, I am on my second battery and it is still in perfect collimation. It cost me $100 but hey, its alive and kicking.

Take the time to collimate you collimator...

OK, cornball commercials aside:

3. It is my understanding that Schmitt Newtonians require a somewhat different collimation technique than standard Newtonians because they have a spherical mirror rather than a Parabolic mirror and that added corrector plate.

http://web.telia.com/~u41105032/kolli/kolli2.htm#schmidt

Nils Olof Carlin is the guy when it comes to collimating Newtonians and the guy who invented the Barlowed Laser that so many of use use with our F/4 scopes.

4. Take your time with collimation and try to be patient. There are lots of reasons that a scope will give lousy looking spiky stars and most of them have nothing to do with the quality of the optics.

What is necessary to get those pin-point "refractor-like" stars.

- Decent optics

- collimated optics

- a scope that has reached thermal equilibrium. Until the mirror and the rest of the scope cools down, things are going to look rough at higher magnifications. Things warp, mini-mirages form inside the scope... Cooling down a 10 inch scope normally takes at least an hour under ideal circumstances, sometimes it never cools..

- good seeing. seeing is the stability of atmosphere you are looking through. when you see the stars twinkle, they twinkle because the air column is refracting the light path. When you see them twinkle naked eye, imagine what they look like magnified 200 times...

good seeing is not the norm.

Jon