Not knowing much about a Cirkut except that it's a panning camera, I'm assuming that the lens rotates in space and there's a film transport that runs at the same time to expose a slit continuously... which means the lens would need to rotate about its FRONT nodal point so as to not change perspective throughout the scene. Same principle as used when stitching photos - you rotate about the front nodal point so as not to introduce parallax errors. The rear nodal point is relevant only with respect to the details of the film transport.

Definition of Nodal Points.