No problems mate, but Ill garentee you that if you do that string trick you make the adjustment its done. I don't like doing things that don't have a solid base line to work from and hence if you use the string method i spoke about your tube will be aligned no ifs or buts.
Also for visual you don't need to be mm perfect it does not matter. My newts mirror is not central I know it isn't i can see that it clearly is to one side, I know the effect it has on my images as the center of the light cone is ever so slightly off to one side. But i need to make a part to sort that out properly which will happen in due course!
Good luck
Brendan
