An apparatus and a method are disclosed for optically determining a distance r to a feature from an origin or a center. The apparatus uses a beam generation unit for launching a reference beam on a reference path and a first beam on a first path. The center from which distance r is determined is selected such that it is along a line of the reference path and not along a line of the first path. Alternatively, the center can be chosen not to lie along a line of the reference path. A rotation mechanism rotates the reference path and the first path about the center such that the reference beam moves over the feature at a reference time t.sub.r and the first beam moves over the feature at a first time t.sub.1. A determination unit determines distance r between the center and the feature from an angular velocity .omega. of the reference beam over the feature and from times t.sub.r, t.sub.1.