Nikon TM 5X Objective Extension Distance Help

[Sippyjug]

I recently purchased a Nikon EDF20050 TM OBJECTIVE LENS 5X and I understand it to be a 'Finite' objective with a 160mm extension distance required (is this correct?). I am quite familiar with using both finite and infinite objectives and when using the finite objectives rated at 160mm that the overall distance is measured from the camera's sensor plain to the tip of the objective or 150mm to the objective thread shoulder.

The Nikon TM objective is quite large as well as quite long. Part of it extends into the bellows or extension tube which of course is understandable.

My question is, "To what point on the objective is the distance measured for the 160mm?" Is from the sensor to the tip of the objective? Is it from the sensor to the thread shoulder? Is it something else all together?

I have it mounted on a Fujifilm X-T20 APS-C sensor mirrorless camera and I am using a Novoflex bellows or extension tubes.

Thanks in advance to anyone that can be of assistance.

[Scarodactyl]

Probably easiest to adjust the length until you hit the rated mag.

[JKT]

It is measured from the sensor to thread shoulder, BUT it is not 160mm. Instead it is 160mm-10mm = 150mm.

[ray_parkhurst]

I think the MM objectives are part of the 210mm system, not 160mm, so the extension required for rated mag is 200mm from the sensor to the thread shoulder plane. At least that's what gives my 5x objective exactly 5x magnification.

[Macro_Cosmos]

Honestly speaking, the best way would be the ruler liveview method. I attempted 148mm to get my ITL200 to infinity, ended up being several rotations off anyway.

[JKT]

Honestly speaking, the best way would be the ruler liveview method.

True. But for a starting point the calculation is useful.