Hi,
My 12" dobsonian is suffering a problem that i cant really understand. I collimate the mirrors perfectly, but as soon as I move it outside of the house to observe, the mirrors go way-off collimation. i've checked the laser collimator and the collimating eyepiece that I use for faults, but they seem to be fine so i've concluded that its the scope. the primary mirror doesn't stay fixed when i move it and i have to collimate it as soon as its outside. I do take extreme care when moving it around, but i can't understand the problem.
Is there a temperature difference between inside and outside ?
Normally this should not give a collimation problem but more blurred images due to temperature differences and that might be your problem.
If yes, store your dob in a shed (if possible) or other location with the same temp as outside.
When you bring the dob from an air-con indoors room, mirror(s) might get dew, so NEVER bring any telescope from an air-con room outside particulary with hot humid tropical like weather.
I had a similar issue with my 8" Dob when I tried to shift the mirror to reduce focal length. I moved it to the point where there was no tension on the collimation screw springs and the locking screws no longer engaged with the mirror housing. Could get it to collimate, but was very unstable. Have repositioned the mirror so everthing is now tight.
Need stronger springs supporting the primary mirror? In my view it should hold collimation with the "locking screws" released. I would only use them during transport (as in "bouncing around" in a car or trailer).
I never collimate indoors. I take scope outside, let it cool down 30mins or so (More if the temperature difference is large) then collimate. Most nights I only use the laser to tweak things, every couple of months I do a full collimation using sight tubes etc.
I chucked away the locking screws, found when I tightened them it moved the collimation anyways. Replaced the springs with Bobs Knobs springs, much stronger and will hold primary securely while scope is being moved.
