They are intended for determination of the location of the nodal point of a Fisheye Lens. In fact, smaller FOV lenses could also be subject to experimentation (except with the third way which requires a VFOV >180deg).
It may be better to look at this site in the following order :
The first one is based on the properties of a LASER pointer.
Even if this a "quick and dirty" experiment it falls in the high precision technique class : it is amazingly accurate. Its main and only drawback is the need to have such a pointer in hand...
By the way this method can also help :
I am sure that some other goodies can also be discovered this way...
I have used this (even simplified) process for the SIGMA 8mm FishEye.
A second method requires to use a nail...
It is less accurate than the first method but it can be used almost readily with so few required equipment.
A third method relies on a mirror.
It shall show the location of a nodal point on a photograph of the lens taken by itself.
Many other surprises were also found with this experiments including the value of the constant ROLL ERROR of the NIKON CoolPix...
A- With a LASER pointer
This is by far the most accurate method that I have yet discovered.
Many of us have such a pointer that is used for pointing at details of an overhead presentation during a conference and before a large audience.
The low powered units cost around 20 to 30 US Dollars and can be bought at an Office Depot store for example.
The LASER power of a LASER pointer is small enough as not to damage the CCD sensor of a camera or its electronics. As a matter of fact its light flux density is much smaller than the SUN shining and burning through your front lens. However this author is not responsible for possible subsequent consequences of the repetition of this experiment by anyone else.
B- With nails and bank-notes
Some EURO bills will be used here to run the experiment.
Anyhow, at the time of writing the author used EURO-ersatz since the EURO bank-note shall be the sole cash currency in Europe but only in 2002 ;-)
C- With a simple mirror
By taking a picture of reflected image of the fisheye lens on a mirror, you shall be able to