Total Track

Total track is the length of the optical system as measured by the vertex separations between the "left most" and "right most" surfaces. The computation begins at surface 1. The thickness of each surface between surface 1 and the image surface is considered, ignoring any coordinate rotations. The surface which lies at the greatest z coordinate defines the "right most" surface, while the surface with the minimum z coordinate defines the "left most" surface. Total track has little or no value in non-axial systems.