Zoning in on perfect (NPP) via Nadir view
Optimal Stitching Position (OSP)
The OSP is not necessarily what people mistakenly call the Nodal Point, nor is it necessarily the point of No Parallax. The position we are after is the Optimised Stitching Position (OSP) where the images stitch together with the lowest possible adjoining control point errors after eradicating erroneous wayward strays and any control points that have been automatically place on object that may have moved between shots. This is highly likely on Clouds, Trees, Cars, Shadows or any non solid structure.
Note: This method is designed around a round rotator/panohead footprint. The method doesn't work with panoheads that leave a square footprint like the Manfrotto range of 303 series panoheads.
LOWER ARM ADJUSTMENT
This is an aid in perfecting your (NPP) No Parallax Point position to find your OSP using your panohead/tripod footprint in the nadir area of your stitched panorama. It will clearly show when you have found the correct centre position and demonstrate how being off as little as 2mm either side of "centre correct position" displays via the panorama nadir footprint.
In this case the Nikkor 10.5mm Fisheye Lens is being used on a Nikon D300 (this will be the same for equivalent 6x 60 degree solutions such as Canon with Tokina or Sigma 10mm etc) on a quality panohead. But it really doesn't matter what the Camera or lens is, you just must be able to see at least some of the "outer edge" of the panohead in the shots but never "all". As this is captured with the Sigma 8mm there is no reason to tilt the camera but I advise you shoot 6 rotational shots at 60 degree click stops for the purpose of finding the NPP and OSP. The first thing is to position your camera on the upper rail and lower rails as close as perfect as you know. Rotate the camera down (15 degrees in this case) "but no tilting required with Sigma 8mm" using the markings on the upper arm rotation markings and lock off tight. Level your panohead at position (1) the 0 degrees starting point. Shoot image (1) and rotate 60 degrees (in this case) to shooting position (2) and shoot - and so on until you have shot all 6 images (because in this case 6 images is the correct number for a set of images using the above mentioned equipment). Do NOT ever re-level between shots. Once done, go ahead and stitch your images and then view the Nadir tripod/panohead footprint area. What we hope to see is a "perfect circle" of the panohead. But most likely it will be out slightly either to the left or to the right showing what looks like a circular saw blade like you see in the images below.
I chose a "tiled floor" for this demonstration because this is many peoples worse nightmare and to prove that once you have followed this mini tutorial that tiles should be of no fear to the panographer.
The above image shows that vertical arm on the lower rail needs to be moved to the right a little.
The above image shows that vertical arm on the lower rail needs to be moved to the left a little.