Optical sensor for collection of point shaped, linear shaped or laminar defects at plane surface area is provided. The optical sensor has telecentric laser scanner (12) comprises a laser (1) for approximately perpendicular lighting of a flat surface area (5), a scanning reflector (2) and a telecentral optics (4) for guiding lighting and detection beams. A detecting unit (11) has a detector opticssystem (8) and a central slit (9), which is positioned concentrically near by the detector optics system in direction of the tele-central laser scanner. A detecting unit also has a super sensitive photo-multiplier for the collection of the scattered light, which runs from defects on plane surface area and a photo-multiplier (6) upstream slit diaphragm (7). An independent claim is also included for a method for collection of point shaped, linear shape or laminar defects at plane surface area.