It seems that the nodal point is "off" the rail---in other words the camera would have to sit back further than the length of the rail allows it to.
Also, when trying to find a nodal point (due to the "distortion" in the lens in VERTICAL position) it skews the picture anyway.
I am extremely frustrated and am about to just quit. I am wondering if I should be testing for the NP with the camera in a horizontal position but that doesn't seem possible iwth the NN 5 with the R16.
I hope someone has some suggestions because I have put in 2 solid days trying to find the nodal point with this lens.
I have PTGUI and wonder if that allows for any mistakes--