A method for detecting a three dimensional object smaller than 300 nm includes providing a light source producing a first light beam (1), the light source being at least partially coherent; and splitting the first light beam (1) into an object beam (2) and a reference beam (6) by a first beam splitter (BS1). An image of the light source is produced in a light source image plane by a first microscope objective (L1), in the optical path of the object beam (2). The three dimensional object to be detected in an object cell (3) is positioned in the optical path of the object beam (2), between the first beam splitter (BS1) and the first microscope objective (L1). The object beam (2) and the reference beam (6) are recombined into a recombined beam (8) by use of optical devices. An optical stop (4) is placed in the light source image plane of the microscope objective (L1) on the optical axis of the microscope objective (L1). Interferometric signals produced by the interaction between the reference beam and the object beam are recorded with a recording device (5). The recombined beam (8) is focused onto the recording device (5) with a focuser (L3). A three dimensional picture of the three dimensional object is reconstructed to be detected from the interferometric signal, thereby detecting the three dimensional object.