Patent ID: 7298487

Claim:
An apparatus for measuring light reflections of an object, the apparatus comprising: (A) an illumination unit for providing an illumination beam ( 305 ), said illumination beam illuminating an illumination field ( 313 ) on the object; (B) an observation unit for providing an observation beam ( 306 ), said observation beam comprising light received from an observation field on said illuminated object; said observation unit comprising at least a first observation field stop ( 310 ) adapted to define a ray boundary of said observation beam ( 306 ); the observation unit further comprising an observation light receiver ( 302 , 304 ) adapted to provide a measuring signal for determining a reflection coefficient from said measuring signal; wherein the apparatus comprises a lens ( 309 ) common to the illumination unit and the observation unit; characterized in that said lens is arranged so that said illumination beam and said observation beam form an overlap therein; that the illumination unit and the least first observation field stop are configured to cause the observation field and the illumination field to have different sizes; and that said first observation field stop ( 310 ) comprises a wall member extending from the observation light receiver towards said lens; wherein the wall member extends only a part of the distance between the observation light receiver and the lens as to limit said ray boundary of said observation beam while maintaining said overlap of said illumination beam and said observation beam inside the lens.