The present invention serves to vary and adjust the transmitted light illumination in microscopes, particularly with respect to the numerous, different illumination situations. The device, according to the invention comprises modules for darkfield illumination, brightfield illumination, and/or diffuse illumination and/or for adapting the object field in which an illumination unit can be selectively coupled to different modules and in which actuators are provided for implementing the adjustments within the modules and for producing the desired connections, these actuators being operated by means of operating elements of a control unit. The adjustments within the modules and the implemented connections are detected and are stored in the control unit so as to be reproducible. The proposed solution makes possible a broad application by means of an ergonomic arrangement of the operating elements and adjusting and/or changing the illumination situations in a simple and reproducible manner.