You asked above if some of my panos are way off while othere are quite good and the answer is yes. But I only have this problem on the bottom and top shot. The bottom shot is always the worst. This is only a problem when shooting things like tile floors or docks. Things with lots of horizontal/verticle lines.
Smooth is definitly correct about the nodal point "moving". In fact we are really rotatating around the nodal point and not "exactly" on it for the reason he stated.
Normally the bottom shot is the closest to the camera. The top shot is further away.
The Angnos rotator is a wonderful tool but it does have a few faults. The small arm that rotates up and down for the nadar and zenith shots does not snap into the 90 / -90 position very well. In fact mine does not snap at all. I have "feel" it and the screw has to be just right or it is too loose or too tight.
It uses a friction screw and a spring loaded steel ball to pop into the hole on the arm. This is a little "sloppy" when trying to get it to aling correctly. You have to be very gentle and feel it slide into place.
There is quite a bit of play in it and you have to mess with it to make sure it is in that position. When the camera is rotated down I can't tell sometimes if it is at exactly -90 deg. I have to eyeball it and i usually make it look exactly verticle. But since we are not supposed to re-level it is important that the down shot be aligned with the other shots. So the down shot must me at "exactly" the -90 deg position on the arm and NOT exactly verticle.
After reading this thread a few more times and thinking about it, I believe this to be the problem. If you don't get the down shot to correctly snap into the correct position then it makes the errors worse. Sometimes I get it right and the errors are very small. Other times they are huge.
I have been sketching a few modification plans for the little arm. We need a more accurate method of rotatoing the little arm. The current design is a little "sloppy". What I mean by sloppy is difficult to get exact. I mean there is play in it. It is not accurate every time. I don't mean "sloppy" construction.
There needs to be a different kind of locking design. One that will pop into the hole and secure the lens from moving. I have problems keeping the camera level at horizontal at times becasue the friction screw doesn't hold very good and if you screw really tight when you get to top/bottom shot the screw is so tight it just shakes the whole rig trying to loosen it enough to rotate.
I have looked at the little spring ball and tried to see if I can push it in with a tool but I cant. It is soooo tight I don't think it is moving at all. On the main verticle arm that holds the little arm there is a deep groove worn into the arm. That tells me there may be something wrong with the tension spring on it.???
So my conclusion is the top and bottom shots MUST be at the exact 90 / -90 position on the rotator and NOT actually verticle.