Hello @P_Tadrous
Thanks for the reply—and I realize my original question may not have been clear.
I’m not trying to access the back focal plane (BFP) outside the objective. I’m using the rear port of a Nikon Eclipse Ti (non‑Ti2) and plan to place a focusing lens just outside that port to focus a collimated laser onto the objective’s BFP (Nikon 100×/1.4 NA oil, HP Plan Apo VC).
What I’m looking for is the nominal optical distance from the rear‑port reference surface to the objective’s BFP along the epi‑illumination path. If this depends on configuration (e.g., filter cube, magnification changer), a typical value, a Nikon drawing/spec, or a practical way to measure it would be extremely helpful.
In a previous post of mine, the value 200mm was suggested, but not with certainty.
Many thanks,
Yossi