An optical system for use in measurements in a sample comprising a light source (102) operable to produce an incident light beam propagating in a certain direction towards the sample (S) through an illumination channel (IC), a detector unit (104) for collecting light coming from the sample through a detection channel (DC), and generating data indicative of the collected light, a light directing assembly (106) operable to direct the incident beam onto a certain location on the sample's plane with a plurality of incident angles, and to direct light returned from the illuminated location to the detector unit (104), the light directing assembly (106) comprising a plurality of beam deflector elements (108 A-D), at least one of the deflector elements being movable and position of said at least one movable deflector element defining one of the selected incident angles.