The film plane is absolutely NOT the same as the entrance pupil (aka "nodal point") of the lens, which is important when shooting stitched panos. To locate the entrance pupil, go to manual or AV mode, set the aperture to f/22, and press the DOF preview button. The entrance pupil will correspond to the location of the aperture diaphragm, which will become visible when looking into the front of the lens with the DOF preview button pressed. It will be between the front element and the lens mount somewhere. With zoom lenses, it will vary depending on the zoom adjustment.
Jonathan, thanks for the clear answer on this. Out of all the web pages I've read, your statement is the only one that has clearly stated just what the nodal point is and how to find it.
The aperture diaphragm is something I can understand as opposed to entrance and exit pupils that was rather confusing, as I didn't know what part of the lens they were talking about.
I can clearly see this on my Tamron 28 - 200 zoom when I was checking it, but still find it really tough to judge where it is in the lens for sure. All the lens elements really give a lot of optical illusions about where things are in the lens.
At least I know what to look for now, so this gives me a good starting point. I will need to build something for my tripod though to better adjust my camera.
With some work I think that for the horizontal rotation to keep it centered on the nodal point shouldn't be too tough.
I'm really having trouble thinking of a way to keep the nodal point constant though if I wanted to shoot multiple rows where the camera was also tilted / rotated up and down. It seems almost impossible to get that one exactly right. It would require a pivot point right in the center of your lens. I guess a pivot point directly below the nodal point of the lens would be as good as you can do, but that has me stumped.
Are there any good plans / products (hopefully cheap) that would maintain the nodal point for both horizontal and vertical adjustments, while shooting one multi-shot scene?