Device and process for determining a distance to an object. The device includes a low coherence light source, at least one lens arranged to focus light from the low coherence light source onto the object and to collect light reflected and scattered from the object, and a window arranged between the lens and the object. An apertured element includes a circular aperture structured and arranged to form a circular light beam from the reflected and scattered light, and a detector system is structured and arranged to receive the circular light beam. The detector system is sensitive to light beam diameter. Further, a determining device is structured and arranged to determine a distance to the object based upon signals from the detector system.