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"Yes here is a link to the solution. http://archive.bigben.id.au/tutorials/360/photo/nodal.html it helps if you have a camera rail to make this measurement. \n  \nhttp://www.ebay.com/itm/Slide-Bar-RAIL-for-CHA-CHA-Stereoscopic-Single-Camera-3D-Calibrated-Tripod-Ready-/381975930317 \n  \nThe measurement is from the back face of the lens (where the lens face meets the camera face)(see below) to the nodal point.  \n  \n  Lens Focal Length Entrance Pupil Length (L2) \n \nOriginal equipment \n(Lenses from same manufacturer as camera) Enter the exact lens name, or if you are using a camera with a fixed lens the name of your camera as mentioned at DPreview. \n \n Facing the side of the lens, the distance from the base of the lens to the Entrance Pupil. A negative value means the entrance pupil is outside the lens, in the camera body. Such is the case with many telephoto lenses. The lens base is the point on the lens that contacts the \"lens base\" on the camera used to determine the \"Tripod mount length (L1)\" in the table above. \n"
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