This disclosure relates to method of enhancing the three-dimensional detection range of a vision-based, single camera intrusion detection system within a tensile test machine or other materials testing machine. Illumination sources are offset from the camera and provide a cones of illumination which intersect with the conical viewing zone of the camera thereby defining a detection zone. When objects intrude into these conical regions, a shadow is cast. The shadow is detected by the camera. The detection of the intrusion is typically used as a safety function to deactivate at least part of the function of the materials testing machine.