Apparatus and method for measuring the curvature of a surface

Apparatus for measuring the curvature of an at least partially reflective surface (1) of a sample (12), with - a light source (2) for irradiating a light beam (3) - a birefringent element (4) between the light source (2) and surface (1), whose at least one main axis (17) is positioned in relation to the light beam (3) of the light source (2) such that the light beam (3) (the light source 2) in at least two parallel partial beams (6, 7) is split, which (to the surface 1) are irradiated, - reflected to a detector (5) for detecting from the surface (1) partial beams (6, 7), characterized by an optical system between the light source (2) and a birefringent element (4), which increases the sharpness of the spots produced by the partial beams on the detector.