The No Parallax Point (NPP) or Entrance Pupil can be considered as the point at which the rays entering the lens converge. It can also be considered as the centre of perspective of the lens or the Apparent Pupil. For some lenses this is a single point, but for others, such as Fisheye Lenses, the location changes with the angle of the incoming ray.  

To achieve the best result when stitching multiple images to create a 360° Panorama, such as with PTGui, it is necessary to rotate the camera about the NPP.

There are a variety of methods for determining the NPP, or desired NPP, for a lens as mentioned in Finding the Nodal Point of a Lens and of these I consider that posted by Garry George using a Cross Line Laser to be the easiest, quickest and most accurate. 

Examples using these methods can be found at Mapped No Parallax Points.

January 2025