# Nikon Eclipse Ti back port to Back Focal Plane distance specification needed

**URL:** <https://forum.microlist.org/t/nikon-eclipse-ti-back-port-to-back-focal-plane-distance-specification-needed/3204>\
**Category:** Hardware\
**Tags:** widefield, nikon\
**Created:** [August 15, 2025, 3:27pm UTC](https://forum.microlist.org/t/nikon-eclipse-ti-back-port-to-back-focal-plane-distance-specification-needed/3204 "2025-08-15T15:27:07Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![Yossi\_Steinberger](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.microlist.org/yossi_steinberger/32/1272_2.png) [@Yossi\_Steinberger](https://forum.microlist.org/u/Yossi_Steinberger)\
**Post date:** [August 19, 2025, 2:49pm UTC](https://forum.microlist.org/t/nikon-eclipse-ti-back-port-to-back-focal-plane-distance-specification-needed/3204/3 "2025-08-19T14:49:23Z")

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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.

> [@Coupling lasers to a widefield microscope?](https://forum.microlist.org/t/coupling-lasers-to-a-widefield-microscope/1979):
>
> Dear μforum - I have a Zeiss Axioobserver microscope, and a EMCCD camera, and wish to purchase a laser light source, and to set up a single molecule imaging system in my lab (I am a PhD student). However, I am ignorant of a good way to couple the lasers to the microscope. In particular, I want to use the 100x, 1.4 numerical aperture objective, and to achieve a maximum power of 30 kW/cm^2 with a far-red laser of ~640nm, but to achieve much lower powers of 30 W/cm^2 with a 405nm, 488nm and 549nm…

Many thanks,  
Yossi

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