An aperture stop device is provided for use in a microscope with at least one adjustable observation parameter. The aperture stop device includes at least one aperture stop (50a, 50b) with an adjustable aperture, that is to say with an adjustable stop opening. The aperture stop (50a, 50b) is adapted to receive an aperture signal representative of an aperture to be adjusted. In addition the aperture stop device includes a control unit (52) for output of the aperture signal to the aperture stop (50a, 50b) in dependence at least on the respectively set value of the observation parameter of the microscope.