1. Locate the nodal point of the fisheye lens of your digital camera

michel.thoby@fnac.net

WHY ?

Many tutorials tell how to locate the nodal point of a fisheye lens, often for the Nikon Coolpix 950, 990 or 995.

The recommanded method given by these excellent tutorials is often (if not always) the same. This standard is coarsely summarized as follows :

"Adjust the longitudinal position of the camera so that two aligned objects (one close from the lens, the other farther away) seems not to move (the first with respect to the second) while rotating the camera. The point of rotation that has this property is the nodal point."

I enjoy stitching panoramas from multi-photograph having had some object(s) VERY CLOSE to the lens. Some call these panoramas "claustropanos".This is generally NOT recommended because more than often Parallax errors will eventually spoil the representation of the foreground. This has been unwillingly verified too many times by myself.

To get acceptable results, I had to spend hours of "creative alteration" (Philo's euphemism for retouching) with my favorite picture editing tool.

To avoid these Parallax errors it is mandatory to rotate the camera around the Nodal Point : it's easier to say that than to do it...

The tutorials were unfortunately of no consistent help for me: the Nodal (Pivot) Point was elusive and seemed to change of location from time to time....

I had to find a solution to definitively locate that nodal (pivot) point !

I got so frustrated that I decided to reverse the standard process : If the two objects are still aligned after rotation of the camera around the Nodal Point, then I imagined that the two objects could move (or be moved) in such a maner as to be both constantly aligned with the Nodal Point.

With this new principle, I managed several ways to moved the pair of points around the lens while maintaining them aligned with the famous Nodal Point when it had been previously located. Thus I kept the camera (and therefore the famous Nodal Point) still.

Then I got (nodally ;-)) disapointed for a while : I had to admit that it is impossible to have this pair of point constantly aligned with a pivot (nodal) point when moving them around the fisheye lens.

The Nodal Point really moves but now I know where and when ! I intend to share this ability with others.

I have developped some rather unconventional experiments which all give consistent results.

They can be reproduced at home by (most) of the CP990 owners and I presume that they can be extrapolated to other photo gears as well.

Experiments for Nodal Point determination.