An optical system for measuring a distance to an object furnished with a plane mirror is disclosed. The optical distance measuring system includes a coherent light source projecting a laser beam, optical elements, and a one-dimensional photosensor. The optical elements split the laser beam into two laser beams and spread out the laser beam into a sheet of light whose orientation is perpendicular to a plane created by the propagation directions of the laser beams. The laser beams are reflected by the mirror and back to the photosensor. The photosensor detects incident light intensity distribution of the reflected laser beams with two local maxima, whose position can be employed to calculate the distance of the mirror and its momentary tilt angle.