Skyliner flextube collimation

[Karen]

I have noticed with my newish 10inch flextube dobsonian that when I have just collimated if I collapse the tube then raise it again the collimation has moved off target again. The metal rods have quite a bit of lateral movement when the clamp screws are not tightened. Once the clamp screws are done up the whole assembly is very rigid.

So I think that maybe the top part of the tube may be repositioning slightly every time it is raised or could it be just the primary mirror moving?

Strange thing is that the secondary mirror always keeps the primary mirror central so it's as if the primary mirror is moving

[Wildwood]

I find that the secondary on mine hardly ever needs adjusting, but I check and adjust the primary on mine each time before I use it. I also find that collimating when the tube is at 45 degrees is best, as if I collimate with the tube upright, it is always out again if I recheck when lowering the scope.

[Stargazer_00]

Just picking this up to save another thread.

In general, how do you collimate a flextube if its dark?

I am saving for a 300p Flextube and appreciate that moving it from shed to garden will likely require collimation but I also expect that its going to be dark when I am getting the scope out to cool, so I don't know how I'm supposed to collimate it.

Is laser collimation the only option here?

[coulthamst]

I find that if I always tighten the rod clamping screws in the same order, starting with the one that is always least firmly "up", and placing my foot on the base and "lifting" the top secondary unit at each rod top as I tighten, I achieve very consistent collimation results. A repeatable order of adjustment/ tightening/ refitting can often improve set-up accuracy in telescope use generally.

[Moonshane]

you should collimate every time you observe (the primary at least) as it will move. I also jiggle the bottom of the tube a little to ensure the mirror is settled. the primary is such a lump of glass it cannot be held too firmly as the optics get pinched and this creates astigmatism.

with even larger mirrors (I have a 16" dob), you need to check collimation occasionally during the night too. it only takes a minute to do it and the views improve markedly.

I use my dim red torch to light the diagonal surface of the Cheshire when dark.

[perrin6]

Just picking this up to save another thread.

In general, how do you collimate a flextube if its dark?

I am saving for a 300p Flextube and appreciate that moving it from shed to garden will likely require collimation but I also expect that its going to be dark when I am getting the scope out to cool, so I don't know how I'm supposed to collimate it.

Is laser collimation the only option here?

I use a torch with my cheshire collimator