Cheap focusser vs. Laser collimation

[Obi Wan Ken00bi]

Dear Stargazers,

I've collimated (if that is a word) my c6 ngt using a laser collimator (if thats a word) I got with the scope, using much of the advice available here on the forums. Adjusted the secondary, primary and secondary again and the results are shown below (bang on !!)

However, if I move my focuser, the collimation gets off completely! (considering how much time I spend getting it in the center)

Is this normal or is my focuser broken? Can I fix this somehow? I'm really happy with my scope (and with the focuser actually since I can get prime focus with my dSLR)

Is this still ok for viewing & AP?

Your help would be very much appreciated

[Obi Wan Ken00bi]

The images somehow got mixed up, the attached picture is after I moved the focuser....

[Scooot]

When you say move your focusser I presume you mean moving in and out? And when you do, it throws the collimation out? In which case It could be its not quite straight. Has the focusser got any little collimation screws on it, sometimes in the corners which will allow you to adjust each side slightly to straighten it up.

[Digz]

As with most laser collimators you need to make sure they ate collimated. A simple rig which allows you spin the collimators whilst pointing at a wall can help. When turning a well collimated laser should scribe a dot, if out it will move and scribe a circle.

Hope that's clear.

[Obi Wan Ken00bi]

Hmzz thanks for the tips guys.

Indeed when I move the focuser in and out it happens, and I can actually see the focuser moving up and down a little bit depending on when I move it in and out. There is a lot of play/ leeway in it. I tried tightening some screws, but I guess the focuser is a lot smaller then its mount.

[LeeB]

The focuser tube could either be adjusted or the tube refelted to remove as much slop as possible. And remember the reinsertion of the laser next time needs to be consistent. Also the allowable slack in the system gets less as f number reduces, a bit of slop in an f10 system will cause little if any difference, in an f4 its a disaster. Its strange that its not just price or age that affects how a focuser performs I have seen a cheap one perform better than a premiun one.

[Obi Wan Ken00bi]

OK, so I think I'll put some work into the focuser tube then. Disassbleming it and looking whats wrong, maybe the refelting will work.