I'm using a NN3 Mk2 with my Canon 7d and have noticed that when calibrating the NNP by aiming down at the bulls-eye on the rotator, my viewfinder center is off to the right a few mm. This is not due to lower arm settings, since that only determines horizontal offset when pointed 90deg down like this. Is this normal? I would have assumed a camera like the 7d would have a dead-center thread. Is it possible that the NN is somewhat off? I've checked my upper arm rotation and it is definitely pointed straight down and level.
From what I can tell, I may need to get the T-adapter to get things exact...but was under the impression that I wouldn't need this when I bought the NN3 starter kit. I've tried 3 different lenses with same results.
If your camera is mounted in the correct position on your pano head and you do not have parallax, do not put too much emphasis on the location of the rotator when you are shooting straight down. Your rig cannot be considered calibrated if you rely only on pointing the camera straight down. There are so many small variables that come into play. Your pano head could be just a touch off (quite normal due to very small manufacturing variances and tolerances). Camera makers do not care about panorama photographers, so they do not optimize their gear for our use. If your panoramas stitches and you are happy with the results, ignore any offset you see when shooting straight down.
The vertical arm on the NN3 can be twisted slightly -- also there is a pad on the bottom of the arm (there was on mine) which can compress when you tighten the mounting knob and allow the vertical arm to become not quite vertical. I think I took mine off. I can't remember and I don't want to look because I've got it where I want it after many small adjustments.