1. A calibration system positioned within an optical inspection apparatus comprising: a sensor operative to capture an image of an object; a lens defining a focal plane external to the optical inspection apparatus and operative to focus an image of an object onto the sensor, the object being external to the optical inspection apparatus; and at least two calibration fiducials located internally to the optical inspection apparatus, the fiducials being positioned adjacent to the focal plane of the lens; wherein the fiducials are operative to calibrate the sensor.