A method for detecting and controlling supply of an immersion medium into an immersion film region between the front lens of a microscope objective and a preparation, particularly in automated microscopes, using a light source which is reflected into the microscope beam path by means of a beam splitter. The state of the immersion film region is recorded and evaluated in a detection unit of the microscope or a detection unit of the autofocus device through an autofocus signal of the light source and/or a reflection of a modulation object arranged in the intermediate image plane of an incident light illumination, and is transmitted to a control unit for the purpose of a change or an error treatment of the immersion process.