A microscope is provided with a holder for holding a sample carrier, an imaging unit which comprises a first detector and a first imaging optical system for imaging at least one part of a sample held by the sample carrier along a first optical axis onto the first detector, a control unit and a detection unit which comprises an illuminating module, a second detector and a second imaging optical system. The control unit only analyzes the measured values originating from the analysis area by the second detector in order to determine the direction of the change of position of the focus of the first imaging optical system along the first optical axis with the aim of positioning the boundary surface of the sample carrier directed towards the sample side in the depth of field area of the first imaging optical system.