|While it is not entirely essential to accurately position
your camera for each image, it does make things a LOT easier if the lens is
rotated as close as possible around its nodal point. By doing so, you remove
parallax errors which may require a lot of retouching to make things look
right in the finished panorama.
Determining the nodal point of a lens is
quite easy to do visually. You will need two vertical features to use
as reference points e.g. a doorway, flag/light pole, corner of a all etc...
One must be very close to the camera, the other, far away. You will
also need an adjustable tripod pano head or a focussing rail to adjust the
position of the camera relative to the axis of rotation. Accuracy will be in
the order of 1mm for a circular fisheye lens. Accuracy will be greater
with the near object as close to the camera as possible.
The diagram below shows what happens in the three possible situations.
Note that the relative positions of the objects on each side of the gap is
determined from the nodal point of the lens, not the axis of rotation.