An interferometer for generating a digital interferogram or a digital hologram of a surface of a scenery (3, 4) with a digital image sensor for capturing image data of the scenery (3, 4), a deflection mirror with a surface reflecting electromagnetic radiation, the deflecting mirror being set up and arranged in such a way that, during operation of the interferometer, the deflecting mirror guides electromagnetic radiation from the scenery (3, 4) onto the image sensor, and a control and evaluation means, wherein the control and evaluation means is connected to the image sensor in such a way that the control and evaluation means receives the image data from the image sensor during operation of the interferometer, wherein the image sensor is arranged in such a way that the image sensor detects at least a first set of image data of the scenery (3, 4) at least in a first position of the deflection mirror, wherein at least one reference mark (11, 12) is provided on the reflecting surface of the deflecting mirror, wherein the control and evaluation means is set up in such a way that the control and evaluation means calculates a first value for the first position either from an angular position of the reference mark (11, 12) relative to an axis or from a distance of the reference mark from a reference point or from an inclination of the reference mark relative to a path of the electromagnetic radiation from a set of image data detected by the image sensor in the first position of the deflecting mirror and links this first value to the at least one first set of image data, and wherein the interferometer comprises an object path and a reference path, wherein the deflection mirror is arranged in the object path and wherein the image sensor is the detector of the interferometer, characterised in that the control and evaluation means is set up in such a way that, during the operation of the interferometer, the control and evaluation means selectively calculates a sharp image of the reference mark (11, 12) or of the surface of the scenery from a single set of image data. a digital image sensor for capturing image data of the scenery (3, 4), a deflection mirror with a surface reflecting electromagnetic radiation, the deflecting mirror being set up and arranged in such a way that, during operation of the interferometer, the deflecting mirror guides electromagnetic radiation from the scenery (3, 4) onto the image sensor, and a control and evaluation means, wherein the control and evaluation means is connected to the image sensor in such a way that the control and evaluation means receives the image data from the image sensor during operation of the interferometer, wherein the image sensor is arranged in such a way that the image sensor detects at least a first set of image data of the scenery (3, 4) at least in a first position of the deflection mirror, wherein at least one reference mark (11, 12) is provided on the reflecting surface of the deflecting mirror, wherein the control and evaluation means is set up in such a way that the control and evaluation means calculates a first value for the first position either from an angular position of the reference mark (11, 12) relative to an axis or from a distance of the reference mark from a reference point or from an inclination of the reference mark relative to a path of the electromagnetic radiation from a set of image data detected by the image sensor in the first position of the deflecting mirror and links this first value to the at least one first set of image data, and wherein the interferometer comprises an object path and a reference path, wherein the deflection mirror is arranged in the object path and wherein the image sensor is the detector of the interferometer, characterised in that the control and evaluation means is set up in such a way that, during the operation of the interferometer, the control and evaluation means selectively calculates a sharp image of the reference mark (11, 12) or of the surface of the scenery from a single set of image data.