I've noticed during my imaging sessions this week that my declination-drift has been poorer than usual, so I was suspicious that the polar-scope which I use for alignment needed re-setting.
But when I checked it this morning (using the antenna on top of the street-lamp across the road as my reference-point), I found that my target was "wandering" around the reticule as I rotated the polar axis, but never returning to the same point.
After stripping it down, I discovered the problem: the collar which locks the polar-scope's helicoid focusser (see picture) had worked loose, and there was then enough play in the thread that the objective-end was "drooping" under gravity!
After I tightened this collar, the 'scope was good and solid again and when I re-fitted it in the axis, the fixed target described a small circle in the reticule. I've now re-calibrated it so that there's very little movement in the target, and even tightened up some slack in the polar axis whilst I was at it.
For those who need help choosing a setup or want further advice on how to improve their own setup
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