To define a device and a process that allows to shoot Nadir shot with the same accaracy as the other images, then to insert it in a standard Spherical panoramic software (e.g. PTools or Stitcher4) and to get a final panorama without tripod or panohead parts obstructing the picture.
The use of a graphic software tool (e.g. Adobe PhotoShop) in order to retouch the panorama, is then completely avoided.
As restriction on the exposure time duration is not taken into account (e.g. shooting at night) a tripod and a fairly precise panohead is assumed to be used.
The number of images that composes the panorama can be any one needed by the given lens on the camera.
As a consequence to the above requirement :
- The Nadir shot has to be as accurately done as any other. That is to say the nodal point (entrance pupil) shouldbe located at the same very place (in three dimentional field) that it is during the rest of the shootting sequence: on the rotation axis and at the same altitude.
- No obstrusive object sutch as tripod legs or panohead shall appear on the usefull center part of the Nadir to be inserted;
- Tripod legs intrusion on the lateral images lower row should also be avoided.
The principal means are harware setup modifications. But a sequential process has to be also used as well as some rather unusual settings in the panoramic software usage.
In the first place , the vertical braket holding the camera has to able the possibility to reverse the camera on the outside.
The top the tripod head (and/or rotator) shall then not be in the field of view even if the lens is looking the Nadir.
Ways to achieve this are shown on this picture:
And the details are shown below:
Then, a second feature has to be added: it's a deployable arm shall put the bracket way out of the panohead zone but at the same altitude.
This is to avoid the tripod leg to be in the center part of the picture. A brace support the cantilever weight offset and a counterweight (photo gear bag) assures stability.
A movie demonstrates simply the principle (QuickTimeVR Object 500ko).
Furthermore, the accurate position of the lens and of the entrance pupil (nodal point) is aided by the installation of two levelling means:
- A LASER pointer thet can be directed with two degrees of freedom.
- A spirit level to control indirectly the verticality of the optical axis.
The two features (Deployable arm and LASER aided vertical Control) taken as a whole summarize the principle of the presented device.
I personnaly used PTGui during the development of this method.
I think that any other might do as well.
The only specific change to my usual way was to set a mutch smaller field of view for the nadir image inserted part.
This is done at the "Cropping step". I reduced the circle diameter and centering to just put it outside of the tripod legs intrusion.
This shall be illustrated in another page.
The best sequence is:
- To shoot the Nadir image after deployment of the arm.
- To put the LASER pointer directed toward the nadir on the ground and mark it (with a coin, for exemple).
- To get the set-up in the usual configuration by folding of the arm and reversing the vertical braket back to the standard position.
- To move laterally the tripod so as to match again the LASER spot with the mark on the ground.
- To proceed then as usual.
Some pictures of this sequence:
1) Shooting the Nadir (after carefull adjustment of horizontality of the elements)
2) Putting the pointer in the direction where the LASER spot on the ground matches exectly the autofocus center square in the viewfinder.
Mark this point of light on the ground.
3) Folding back of the of the extension arm
4) Sliding the set-up sideways until the LASER spot matches the mark on the ground. (the laser beam is not obstructed by the panohead but one cannot see now the LASER spot on the ground through the viewfinder).
5) Set the panohead for the configuration for the shooting of the lateral images.
Note: With the Sigma 8mm fisheye shown on these picts, I get it slightly upwards so as to improve Zenit definition as well as to get free from the tripod leg intrusion at the bottom of the four pictures.
Some pictures from the processing with PTGui and some images from testing.