[andyc (Andy)]

Hi all,
Much as I'm having a lot of fun with my imaging just now, I'm having a problem I've not encountered before. I think it's tube flex - the guiding is OK, if not absolutely amazing, but over the course of a series of 5-minute exposures, the stars on the actual image drift slowly and fairly consistently across the frame in one direction. They were drifting northeast when the scope was pointed high to the east two nights ago. I use a 150mm Newtonian and Orion mini autoguider.

I've only noticed the issue come prominent recently - and I'm guessing one of two causes: I turned the focuser from being perpendicular to the DEC axis (so more convenient for an eyepiece), round to being parallel with the DEC axis, which balanced the axis much better. I still put a little extra weight on one side of the axis rather than perfect balance.

Or is it because after a break, I'm imaging in colder nights and there's more metal contraction/flex over a night?

The result is that quite a few frames have egg-shaped or downright trailed stars, and though at the turn of the year I was rejecting very few frames indeed from trailing, now I am rejecting 1/4 frames at least, and not ideally happy with some others.

Any suggestions, or tips about tube flex, diagnosing the source, or solutions (assuming that's the cause)? I feel a bit out of my depth working this one out!