My current imaging setup.
53mm extension from Precise Parts
A1260 11.9mm adapter
ADA20132 2" thin nosepiece adapter
Scope Stuff 3mm thick ABS plastic spacer
QSI camera with A2558 nosepiece
This gives the overall back focus of about 85.69mm not counting 3mm thick Astrodon filters. Total "Optical" back focus is 84.69mm. This is an actual measurement with precision caliper.