I won't mention brand names to made the question as generic as possible.
If I have a camera with zoom, and I want to add a certain teleconverter lens, do I need to put in-between a spacer ring, to get the correct magnification factor (i.e. for other reasons than adapting the diameters or distancing the TC from the full extended zoom)?
If so, how does the spacer ring length affect the resulting optics?