I had put a 5mm extension ring directly onto the ZWO camera between the filter drawer and the camera, instead of putting the filter drawer directly against the camera.
I was then moving around and trying to adjust the back focal distance as I wasn't convinced I had it correct for my Celestron Edge 11.
Unfortunately the 5mm extension ring wouldn't come off and being so short could really get a could hold of it.
Even plumbers grips wouldn't turn it....
Armed with Sasha's sliders and WD40, problem solved!
Note to self: Don't put small extension rings where you can't get a proper hold of them...
Anyway, that will do for now!
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