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Well done Doug!! Good to know you will be out observing. I have been through similar issues and learnt a lot by solving them!
I think the lesson to be learnt is that collimation is just one of the things that can go wrong and that it is not a guarantor of good images.
The classic example is trying to fix coma, which is an inherent property of all Newtonians and the best collimated scopes, especially fast ones will still display it.
The clue that it is a focal position error is that if focus is really bad in one position but improves as the focuser is wound, but the focuser runs out of travel before focus is reached, then the distance between objective and EP needs adjusting.
If you move from poor focus to better focus then back to poor focus, the focal length is all good and it is another cause (collimation, astigmatism, poor optics, bad seeing etc) that is causing the poor image.
Malcolm
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