I use a Meade 2 inch prime focus adapter (2 inch diameter barrel with
T-threads in plain English). It seems a bit long for a televue
powermate and I wonder if somebody makes a short (say maybe 1.5 inch
long or less) prime focus adapter that can accept 2 inch filters. BTW,
I suspect the extra length causes a bit of darkening at the edges,
which is why I'm looking for a shorter one.

This lumicon looks good, but it doesn't hold a filter.
Of course, with the powermate, the filter could be placed at the