collimating problems,reflector scope

[solarface]

I recently purchased a used 6 inch celestron nexstar newtonian reflector,also bought a new laser

collimating tool , aligns and ,centers in collimator ,but when I move eyepiece out (extend) laser point moves out

of collimation,,usually about 3/4 of the way extended,,Collimator is pretty heavy,,anyone else had this type of a problem?

Thanks Solarface

[crashtestdummy]

I think its probably just down to the quality of original equipment focusers fitted to scopes.i would say that you are probably best collimating your scope with the focusers all the way in to start with and then seeing how the views look.obviously you aren't going to be able to get it spot on for all travel points in the focuser drawtube so maybe collimate at the point where you get focus with your most used eyepiece.other than that you would need to upgrade your focuser for a better quality one,assuming that the standard one isn't in bad condition i.e. bent out of straight.maybe try adjusting the preload on the drawtube as it may be sagging

[umadog]

I suppose exactly what you choose to do depends on how heavy your eyepieces are. If your eyepieces are comparable in weight to the laser then maybe you should collimate for the focus position of your highest power eyepiece. Collimation becomes critical at high power, and your most used eyepiece will probably be a medium power at which you likely won't notice moderate degrees of mis-alignment. If your eyepieces are light, then collimate with the drawtube racked in.

Finally, by how much does the laser move and where are you measuring this (outward or return beam)? Depending on the focal ratio of your scope (what is it?) the amount it's moving may not be a problem.

[NGC 1502]

Good advice above, but I'd like to add to the comment in post #2 about adjusting the loading on the focuser.

Lots of different focusers out there, but most have screws that can be tweaked to lessen focuser drawtube flop. The focuser on my Dob has two screws, one each side of the main tensioner knob, or sometimes tweaking the screws that attach the pinion to the focuser can lessen any slack. I've also sorted focusers by using thin Teflon tape on the drawtube. I've had a focuser on a 6" Newtonian that had alarming amounts of slack, sorted by tweaking the screws and using tape. If you are a DIY type, I'll bet you can at least make things better or sort it completely.

If you think that Teflon tape will help, drop me a PM with your address, I'll send some, no charge. I see you are in the US, no prob. (a clubmate gave me a roll of the tape).

Hope you sort the issue, Ed.

[solarface]

I tried your ideas,I tightened the rack gear screws a bit on the draw tube,applied a small amount of clear silicone grease to smooth things out,

collimated the focuser at 1/2 and 3/4 extended, which is close to where the most used eyepieces seem to be in focus,,, looked at M31, view seemed clear and brite,

Thanks to all for help . Solar Face,,

[RonVen]

I'm glad it's sorted. I just wanted to add that your scope may have a corrector lens at the bottom of he focuser, which may be playing tricks with your laser.