Swingrod Geometry

This is a simple explanation how "Swingrod" works.

 

Swingrod is a system for handheld panorama.

 

It illustrate the geometries at the angles of depression (left) and elevation(right) of philopod technique.

www.philohome.com/tripod/shooting.htm

 

I usually put a coin on he ground and take four photos above it. You will find a small coin at the nadir of my swingrod panoramas.

 

Angles of elevation and depression should be determined in order to maximize the overlap between the fields of view.

 

Usually the nodal point of circular fisheye is at the center of the lens rim circle. The magnetic coupler is therefore adhered on the rim, but the center of the swingrod does not come just below the nodal point because of the angles of elevation/depression. To rotate the camera around the true nodal point, You must not rotate the camera around the swingrod. This photograph illustrates how to determine the offset. The offset distance of the rod end from the center of the positioning coin (true pivot) should be r sin A, where r is the radius of the rim and A is the angle of elevation.

 

In my Peleng fisheye's case, offset is about 1cm. Coin diameter is used as the guide for eyes.

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  • Grzegorz Rogala 5y

    Wow I'm completely confused now. I always thought you have to rotate the camera around the nodal point of your lens. You say that the Nodal point of your Peleng is at the centre of the lens rim. Would that be true for my Sigma 8mm as well? What happens then if you put the rod on top of the coin? The nodal point of your lens aligns with the true pivot isn't that true? I'm using a similar solution to shoot my panos but instead of a rod I'm using a weight that is attached to my lens with a piece of string. The weight always rests on the ground and I always rotate my camera around the weight's centre which is aligned with the nodal point of my lens. The length of the string is fixed so that keeps the camera's position locked and the bubble level helps to keep the horizon straight in each shot. However, according to your description it seems that I miscalculated the nodal point of my Sigma 8mm. Please tell me more about how to find a nodal point of my Sigma 9mm.
  • Masakazu Matsumoto 5y

    Firstly, I have not calibrated the nodal point of my lens, but I believe it must be at the center of lens rim.

    Suppose you put your camera with fisheye on the XY plane (just put it on a section paper). Let the nodal point of the lens just above the origin, and camera direct to Y axis. Take an equirectangular panorama around the nodal point.

    If camera is on the true nodal point, both x and y axes are projected as vertical straight lines in the equirectangular image. Right?
    On the other hand, the field of view of a circular fish eye is 180 degree, so if camera directs to y axis, x axis must be on the edge in the circular view.

    If you incorrectly put your lens ahead the origin, x axis will be out of view. If lens is behind the origin, x axis will not be a straight vertical line in equirectangular image. Only when the plane of the lens rim is on the x axis, the x axis is projected on the edge of the circular view. Therefore, nodal point must be the center of lens rim. That will be true for all the circular fish eye with accurately 180degree FOV.
    (See the following link for example.
    www.agnos.com/prodotti.htm?v_lingua=ENG&v_iss_web=000... )

    Secondly, if you rotate your camera horizontally, you need not be careful to the offset. But, philopod technique requires the angle of elevation/depression to cover both zenith and nadir with only four shots. You see, in my swingrod's case, the rod is attached at the bottom of the lens and if the lens is banked, the rod moves ahead/behind the center of the lens. Simon S. cogitated to attach the string not at the bottom but at the side of the lens (He denote it "Y-string") That is another way to avoid the offset. (Sorry his page is now missing)
  • Masakazu Matsumoto 5y

    I found a description on the no-parallax point of Sigma 8mm in the following link:
    michel.thoby.free.fr/Blur_Panorama/Nikkor10-5mm_or_Sigma8...

    It shows that the NPP depth depends on the angle. My estimation is correct at angle of view = 90 degree (i.e. side end of view) but inaccurate in average. Average NPP is located at 18mm behind the lens top.
    michel.thoby.free.fr/Blur_Panorama/Nikkor10-5mm_or_Sigma8...

    I will find information on Peleng 8mm.
  • Grzegorz Rogala 5y

    Thanks a lot that's really helpful
  • Jeffrey Martin 5y

    Uh, sorry but this explanation really isn't helping me. i know and use the plumb-bob/string (Philipod) technique, but WTF is this swing rod all about? ? :-) Is there another explanation somewhere? :)

    thanks!
    Jeffrey
  • Grzegorz Rogala 5y

    A swingrod is that thing on the picture above attached to the lens. It's a variation of a virtual tripod used to shoot 360 degree panoramas without using an expensive panoramic head. Google it or find discussion groups on flickr for more info
  • kistuszek 2y

    Its the same, just the string is a rod, so it wont get tangled. The rod needs a weight on the end and a good pivot point close to the lens like if it was a string.
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Taken on May 20, 2010
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