1. An apparatus for optical determination of distance to a feature, said apparatus comprising: a) a beam generation unit for launching a reference beam on a reference path and a first beam on a first path; b) a rotation mechanism for rotating said reference path and said first path about a center along a line of said reference path and not along a line of said first path, wherein said reference beam moves over said feature at a reference time t r and said first beam moves over said feature and at a first time t 1 ; c) a determination unit for determining a distance r from said center to said feature from an angular velocity ω of said reference beam over said feature and from said times t r , t 1 .