Photophys.com: The Science of Photography

Those who capture photographic panoramas need to know the No Parallax Points (NPPs) for their lenses. The NPP is often referred to as a nodal point, but that is a misnomer. In fact, every lens has two nodal points, and neither is relevant to this discussion. The proper rotation axis for a panoramic photograph lies in the entrance pupil of the lens. If one rotates the camera around this axis when taking photographs, then the images can be stitched together accurately so that even close-up objects will be properly represented.

Now I come to the crux of the matter. I have a Canon 15-85mm EFS lens, and I need to know where the NPP is. If one is lucky the NPPs can be found online. Some lenses appear in the Nodal Ninja or Panotools sites. However, my 15-85mm lens is too new to be included. The only recourse is for me to determine the NPPs for myself. The crudest determination is to look into the front of the unmounted lens to see where the entrance pupil appears to be. About the only thing this procedure reveals is that the NPP is close to the front of the lens at 15mm and that it recedes rapidly as the lens is zoomed to 85mm. The measurement of the NPP requires something more precise.

There is no shortage of advice about how to determine NPPs online. For example this video describes the operation. Basically the rotation axis must be chosen so that near by objects and distant objects will maintain their relative positions in the image as the camera is rotated. This is a bit more difficult than it might appear. Fortunately, I have a Nodal Ninja 3 tripod head which makes this operation relatively easy.

In this measurement the camera is held in the vertical position and the image is viewed through the viewfinder or better still with Canon Live View and magnification. I rotated the camera around both vertical and horizontal axes. For horizontal movement I used near and far candles on a table, and for the vertical rotation I used rulers held in place by books on a bookshelf. This is a trial and error measurement made by sliding the camera back and forth or a rail, and I think the results are accurate to about 10%.  Here is the pdf file: table of NPP values.  If you find discrepancies, please let me know.

You will find that accurate NPP values are important when nearby objects appear in an image. If everything in the images is far away even handheld rotation will work for panoramic photography.