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Matteo Cominetti is a design technologist focusing on BIM, VDC, parametric design and open standards.


Detect the nodal point of your lens [How to]

*EDIT: In the following article I am erroneously talking of “nodal point” but the correct term is no-parallax-point or entrance pupil, infact:

The nodal points are widely misunderstood in photography, where it is commonly asserted that the light rays “intersect” at “the nodal point”, that the iris diaphragm of the lens is located there, and that this is the correct pivot point for panoramic photography, so as to avoid parallax error. These claims are all false, and generally arise from confusion about the optics of camera lenses, as well as confusion between the nodal points and the other cardinal points of the system. The correct pivot point for panoramic photography can be shown to be the centre of the system’s entrance pupil.

You can get more info about this at: Cardinal Point (optics) You can check a database of Entrance Pupil Measurements*

As an amateur photographer I love taking panoramic pictures, as you can see from my VR images. In order to take such panos it’s mandatory to rotate the camera by its nodal (or pivot) point, especially when you are in small rooms. The nodal point is something like the human pupil, it’s the point around which the pictures have no parallax effect.

There are several ways to find this point; since we already know 2 coordinates (the point certainly is on the longitudinal axis of your lens), we just need to know how distant it is from the front lens, usually 1-2 cm.

A good method consists in using a laser:

  1. detach the lens from the camera and put a vertical sheet of paper few centimeters distant from its back (here the laser ray will be projected)DSC_0076_e
  2. tape some other papers on the table (this is where we’ll be drawing the lines)
  3. tape the laser to the square (our cursor), and put it on the papersDSC_0078_e
  4. check that the height of the laser ray matches the one of the lens axis
  5. don’t forget to mark on the paper the position of the front glass of the lens
  6. now try different angles with the cursor (and draw lines), always pointing it to the center of the lens, so that you see the red dot projected behind the lens
  7. finally pick up the lens, join all the lines, and you’ll find the magic point![DSC_0080_e](/assets/2010/04/DSC_0080_e-300x200.jpg "DSC_0080_e")DSC_0079_e Depending on the accuracy used (mine was not much) you will see the line crossing in the same point, the distance from it to the front glass of the lens is what we were looking! After doing so, you can start planning your homemade panoramic head.

Thanks for the method to Michel Thoby. Other methods can be found here.

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