An ink sensing system for a vector plotter in which a pen is adapted to be raised and lowered from a drawing media surface along a system axis. An optical detection system is provided which has a focal point on the system axis and below the media surface when the pen is in its lowered position and at the media surface when the pen is in its raised position. The optical detection system includes a source of illumination and a detector system to determine the degree of reflectance from the media surface to indicate the presence or absence of ink on the media surface. In a particular embodiment the optical detection system is moveable and the movement of the optical detection system is coupled to the movement of the pen. Furthermore, the focal point of the optical detection system coincides substantially with the last point of contact of the pen with the media surface when the pen is in the raised position.