Microscope and method for generating an overview image of a sample

A microscope, comprising:

• an optical system comprising an immersion objective which is configured for an immersion medium of a predetermined refractive index;
• an aperture stop;
• and
• a processor configured to set an immersion-free imaging mode in which the optical system is operated without immersion medium,
• wherein the processor is configured to control the aperture stop in the immersion-free imaging mode to set a numerical aperture of the immersion objective to a reduced value which is lower than a nominal value of the numerical aperture, the numerical aperture being equal to the nominal value when the optical system is operated using the immersion medium without reducing the numerical aperture by the aperture stop, and
• wherein the processor is configured to control the optical system in accordance with the reduced value of the numerical aperture in the immersion-free imaging mode to generate at least one image representing the overview image of the sample.