Panoramic stitching and nodal head adjustment: Completely eliminate parallax by locating the lens nodal point

1. What is Parallax? Why does it cause the panoramic splice to be completely scrapped?

Do a simple human optical experiment:

• Put a finger 20 centimeters in front of your eyes, close your left eye and look with your right eye, your finger blocks something in the distance;
• Keep your fingers and head absolutely still, close your right eye and look with your left eye instead, you will be shocked to find: The position of your finger relative to the background object has a huge lateral misalignment jump!
• The root of disaster in panoramic splicing: When you screw the camera directly onto an ordinary tripod to rotate and pan to shoot multiple panoramas, the center of rotation is the tripod screw hole at the bottom of the camera (away from the inside of the optical axis of the lens). The camera position is actually drawing an arc. At the point where the rotations overlap, the railings and trees in the foreground undergo physical parallax displacement relative to the snow-capped mountains and buildings in the distance. The post-stitching software (PTGui or Photoshop) cannot geometrically and mathematically align the foreground and background at the same time, and can only stitch the railings into horrible double ghosts or broken truncation!

2. Core physical truth: lens entrance pupil (Entrance Pupil/node)

To completely eliminate parallax, when the camera rotates and translates, it must and can only use the optical "entrance pupil" of the lens as the geometrically unique center of rotation**!

• Geometric definition of the entrance pupil point: Looking from the front of the lens, the optical position of the virtual image presented by the aperture blades after refraction of the first set of lenses.
• When the rotation axis strictly passes through the center of the entrance pupil point, no matter how the camera rotates left and right, the relative occlusion relationship between the foreground object and the distant object remains geometrically unchanged, and the parallax is completely zeroed!

3. Practical three-step method for finding the entrance pupil point on the two-way panoramic rail (Nodal Rail)

1. Installation hardware: Install the panoramic indexing plate on the tripod, install an Arca two-way metal front and rear slide rail about 15-20 cm long above, and fix the camera vertically on the slide rail clamp.
2. Place two reference objects for the close shot and the distant view: Find two slender reference objects indoors (for example, stand a vertical chopstick A 1 meter away from the lens, and find a vertical edge B of the door frame 5 meters away from the lens). Adjust the camera position so that chopstick A and the edge B of the door frame completely overlap in the center of the viewfinder.
3. Left and right rotation test and front and back sliding fine-tuning:

• Rotate the tripod to the left to move the reference object to the far left edge of the screen; then rotate it to the right and move it to the far right edge.
• If when rotating to the left, the nearby chopstick A moves left and right relative to the door frame B, it means that the camera rotation center deviates from the entrance pupil point!
• Loosen the slide rail clamp, slide the camera back and forth to fine-tune its position, and repeat left and right rotations, until no matter how the camera rotates left and right, the chopsticks nearby and the door frame in the distance overlap perfectly at any edge of the screen, without any relative displacement!
• At this time, the millimeter scale marked on the slide rail (such as 72mm) is the absolute no-parallax entrance pupil point scale of your lens at that focal length. Record this value, and then take any panoramic shots of indoor narrow spaces or grand city buildings, and the stitching success rate will be 100% flawless.