How to shoot a Nadir image for a spherical panorama with a rectilinear lens?

Question

Trying to shoot a complete spherical panorama, I found that no software was able to stitch correctly the nadir images I had. PTGui Pro 9.1 and Autopano Giga came close but no cigar as they say. I found a vague mention that says is is possible in an answer to this question which says:

There is of course a way to shoot nadir and zenith with a tripod to eliminate it from the picture but believe me it is extremely complicated and involves moving the whole tripod several times.

This brings me back to my question:

How to shoot a Nadir image for a spherical panorama with a rectilinear lens?

For one, I do not have a fisheye lens. Plus, this severely limits the resolution of resulting panoramas, so I really want a solution that works with any rectilinear lens, although most importantly between 12 and 55mm on an APS-C sensor or 16 and 75 on a full-frame, since those are the most common focal-lengths I have with cameras of the respective sensor sizes.

Answer 1

There's a tutorial on Panoramas.dk where the basic idea seems to be using a hanging locked measuring tape from camera to spot marked on ground with a lens cap to make sure you can hang the camera on a slanted support so that its nodal point is in exactly the same place where it was on tripod; you also have to watch out for shadows created by your support (so pick a suitable angle).