Simple panoramic head to put the nodal point on the axis of rotation
		The previous Technical Note established the importance of positioning the nodal point of the lens on the axis of rotation. This eliminates parallax errors and ensures that when we come to the stitching of separate images the left hand side of one will closely match the right hand side of the next (after remapping to cylindrical perspective). This does not require expensive equipment; the device shown alongside was made from two flash brackets and an old ball and socket head.

The horizontal bracket (in this case a metal casting) is rigidly attached to the socket by a bolt into the existing tapped hole. A second flash bracket (fortunately this one is mild steel) is bent at 90º to support the camera vertically and the two brackets clamped together using a knurled headed screw into the tapped hole of the bent bracket. The original clamping screw of the ball and socket head is still effective in clamping the panning motion and the camera clamping screw allows adjustment of tilt.

A 360º protractor clamped under the head, and a wire pointer attached to the rotating bracket allow accurate measurement of angle of rotation.

Setting up

You will not find a mark on the lens to indicate the position of the nodal point, so you have to find it by experiment. To position the camera so that the nodal point of the lens is on the axis of rotation, the following procedure is suggested:

Position the camera indoors (on the tripod and panning head) so that you can view a nearby vertical edge of a door intruding from the left against a distant vertical edge of a window intruding from the right (or vice versa). If the camera is now moved to the left or right you can find a position where the door just obscures the view through the window. To get a feel for what we are looking for it is a good idea to first position the camera at one extreme position on the bracket, say as far back as possible. As the camera is rotated compare the appearance of the edge of the window when it is at the extreme left of the frame with when it is at the extreme right of the frame. The door appears to move relative to the window.

Without moving the tripod, move the camera forward along the bracket and try again; the effect will be reduced. If you move the nodal point so that it is as far forward as possible it should be in front of the axis and the relative movement of door and window will be reversed.

The correct setting is when the door does not move relative to the window as the camera is rotated. Finally view the camera from the front to check that the lens is centred over the axis.

Note that the camera position will be different for lenses of different focal lengths.

Technical Notes

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