With a truss, it can be way off each time. That's possible and not necessarily a sign of a flaw.
The focuser alignment and secondary "down" offset often don't move since they are fixed in the upper cage. I don't bother checking my secondary offset placement except occasionally, if it hasn't migrated in several sessions. DItto with focuser squaring.
But the relationship between the primary and the upper cage will be off with trusses when you reassemble. A bit of temp change, some wear on a metal fitting, some slight (undetectable) bow in a truss tube, and voila, you are off by half a mirror diameter on the primary collimation.
Checking the tightness of the spider vanes is worth doing, as a stripped or loose screw there can often explain collimation volatility.
And the primary will normally wiggle in the cell with transport. Not a flaw, just reality. But check the tightness of the primary collimation bolts and springs...Some bolts come loose and aren't actually holding the cell together..the mirror can "flop" with changes in tube position. Get down and study the thing and it should make sense after a few minutes.
I've a telescope with an identical cell to the LB, altho mine is a different vendor. Do you have locking bolts in addition to primary collimation bolts? If so, be aware if you collimate, then tighten the LOCKING bolts, that the collimation will CHANGE. I don't recall seeing much on this in print, but it does change. My webcam-collimation experience (see Articles section) proved this to me. I got the colimation with the barlowed laser dead on, then tightened the locking bolts. Even with mild tightening, the center mark migrates a full diameter away. So, either don't use the locking bolts, or recheck after you lock the bolts to fine tune.
But, yes, enlisting the assistance of a veteran Newt user is priceless and very efficient at your phase in learning the process. In truth, we're all learners, all the time....
Regards
Scott
Quote:
Originally Posted by a1120028
Well after watching the tutorial on andyshotglass page I gave it a go and boy was it out a mile. It is all centered and aligned now, the articles are right insofar as actually doing it a few times makes the whole thing more comfortable. I can not believe I sent it back to the shop to be collimated and just by moving it to my house it went out by so much. It was that bad that a return laser did not even hit the secondary. I suspect the shop played me for a fool and they would not be far off as I know next to nothing about telescopes atm.
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