1. Apparatus for determining the distance D of an object with respect to a reference location comprising: illumination means for projecting a preselected feature upon the object along a first direction from the reference point to the object, said feature having at least two distinct points separated laterally by a distance h measured transversely to said first direction, means positioned at said reference location for generating an image of the feature reflected from the object, said image generating means including a thin lens with a focal length F, said image at the focal plane of said lens having a spacing between the image of said at least two distinct points of h.sub.i, and processing means for comparing the reflected image h.sub.i of the feature with the preselected feature h to determine the distance D where D=hF/h.sub.i.